Priority Pitfalls – detailed analysis

The ability of a party filing a patent application to “claim priority” from the filing of an earlier application is enshrined in Article 4 of the Paris Convention of 1883. At first sight it appears a simple matter for the applicant for the original application, or their successor in title, to claim the benefit of the earlier filing date for the same invention. However, questions have arisen over the years as to the conditions which must be fulfilled for the priority claim to be validly made. In this update, we review recent developments in the case law of the European Patent Office and the UK Courts in this area.

The party entitled to claim priority

Who may claim priority?

Article 4A of the Paris Convention says that “Any person who has filed an application for a patent … or his successor in title, shall enjoy … a right of priority”. Where no succession in title occurs and an application claiming priority from an earlier application (i.e., the “priority application”) is filed by the same party who filed the priority application, it is clear that the party enjoys this right to claim priority.

However, difficulties can occur if there has been a transfer of ownership of the priority application and/or the associated right to claim priority, before the filing of the later application. If there has not been a correct transfer of ownership and the later application is filed by the new party, that party might not actually have the right to make the priority claim. This can be fatal to the validity of any subsequent patent, if there is damaging prior art published during the period between the priority date and the filing of the later application.

Who owns an invention and the right to priority?

In the absence of any additional provisions, an invention belongs to the person who invented it. The party who owns an invention is the party entitled to have a patent granted for it.

In many countries in the world, if an inventor is employed and he makes an invention in the course of his employment, statutory law provides that the invention is automatically owned by the employer, in the absence of any agreement to the contrary.

When filing a priority application in most countries, therefore, the application is usually filed in the name of the employer. The filing of an initial priority application provides the applicant with the right to claim priority from it, as stated in the Paris Convention. Therefore, when the employer subsequently files an application claiming priority from the priority application, the applicant on both cases is identical and there is no question that the priority has been validly claimed.

However, the situation has been somewhat different in USA. There, until recently, patent applications had to be filed in the name of the inventor(s). The question then arose, if a subsequent non-US application were to be filed (for example a PCT application), in the name of a company rather than the inventor(s), whether the company was a “successor in title” as mentioned in Article 4A of the Paris Convention, such that the right to claim priority from the priority application had been transferred from the inventor(s) to the company.

Provided an assignment document had been completed by the inventor(s) and the filing company in the period between the priority date and the date of filing the subsequent application, this was not in doubt. Problems arose, however, if an employer relied on an employment contract to effect the transfer of the entitlement to be granted a patent and of the priority right. Typically, of course, an employment contract is signed before any invention is made by the employee, so the question is whether such a contract can result in the transfer of rights arising from an invention made in the future.

Several cases in the US Courts have indicated that a statement in an employment contract of an “obligation to assign” future inventions would be unlikely to be sufficient proof that actual, legal, transfer of ownership of the application (and the associated right to be able to claim priority) has taken place. Wording such as “agree to assign and do hereby assign” is more likely to be effective. See, for example, DDB Technologies, L.L.C. v MLB Advanced Media, L.P. (517 F.3d 1284, 1290 (2008)) and Stanford University v Roche (Fed Cir. 2009, case 2008/1509, -1510).

Of course, if there is no employment relationship and no assignment has been completed between the filing of the priority application and the filing of the later application, then the invention, the application and the right to claim priority all remain the property of the inventor.

This is also the case if there has been a transfer of ownership from a company which was the applicant on the priority application, prior to filing the priority-claiming application. In order for priority to be claimed by a different party, the assignment of the right to claim priority must have been completed before the later application is filed. European Patent Office decision T577/11 confirmed that a subsequent assignment, stated to have retroactive effect, is not sufficient.

What if legal transfer has not taken place?

There have been cases both at the European Patent Office (EPO) and in the UK Courts which considered the effect of a failure to formally transfer the right to claim priority, before the priority-claiming application was filed.

At the EPO, in case T62/05, evidence was submitted of the intention of the priority applicant to transfer rights relating to the priority filing to the European patent applicant, although an assignment document was not completed until after the European application was filed. The Board in that case concluded that, since priority rights can be assigned independently of the corresponding application, this was not sufficient evidence that the priority rights had actually been transferred. In this decision, it was held that only a formal assignment document, mentioning the priority application by number and including reference to transfer of priority rights (rather than just the application itself), would have been sufficient proof. The European Patent Convention (EPC) requires that an assignment agreement is signed by all parties to the agreement, not just the assignors (Article 72 EPC).

In the UK, the case Edwards Life Sciences AG v Cook Biotech Inc. (EWHC 1304 (Pat); referred to here as “Edwards”) concerned a similar issue. The Judge in the case concluded that Cook was not entitled to claim priority from the initial US priority application. The US application had been filed in the names of the three inventors, only one of whom was an employee of Cook. Cook was the sole applicant for the priority-claiming PCT application. The share of the ownership of the employee inventor of the priority document did automatically transfer as the result of the employment agreement, but the other two inventors had not assigned their shares to Cook until after the PCT application had been filed.

Furthermore, there was no assignment from the non-employed inventors to the employed inventor. As explained in EPO Decision T788/05, in the case of joint applicants, “… the priority right belongs simultaneously and jointly to the two applicants, who thus constitute a legal unity unless one of them decides to transfer his right to the other applicant, who then becomes his successor in title …”

Therefore, Cook was not a successor in title to all three inventors at the time that the priority claim was made, so the priority claim was not valid; this could not be rectified after grant. In consequence, the patent was invalid as a result of the relevance of an intervening publication.

As might be imagined, these decisions caused some anxiety to applicants and their legal advisors, as checks were made in files as to whether the priority had correctly been claimed. At Greaves Brewster, we filed several successful applications at the EPO requesting a correction of the applicant, in order to restore the effectiveness of the priority claim.

Transfer of equitable title may be sufficient

More recently, however, several decisions appear to have moved the high-water mark down somewhat on this issue. There are several EPO Board of Appeal cases, for example, which expressly disagree with the reasoning and conclusion of T62/05 outlined above.

For example, decisions T517/14 and T205/14, near-identical cases relating to a parent and a divisional application in the same family, criticised T62/05 for being too restrictive. In these cases, the priority applications were filed in USA in the names of the inventors. The priority-claiming application was filed in the name of the company which employed the inventors. No assignment document had been completed between the filing of the priority application and the later, priority-claiming one.

The decisions note that Article 72 EPC, relied upon in T62/05, relates to the requirements for assignment of a European patent application, not for the assignment of a right to claim priority. In the absence of a formal document transferring the right to claim priority, a deciding authority is entitled to examine other available evidence to determine whether, on the balance of probabilities, the priority-claiming party has proved that the right has been transferred. The Board considered that it is a question of national law as to whether the right to claim priority has been transferred to the claiming party.

In those decisions, the relevant law was found to be the law applicable to the legal relationship between the inventors and the company which claimed priority. The law of the country in which the priority applications was filed, USA, was not relevant. Therefore, the relevant law was that of Israel, since the inventors were employed in Israel by an Israeli company. Israeli law is similar to that of many countries, in that an employer automatically owns an employee’s invention and associated rights, unless some agreement to the contrary is made.

Furthermore, in J19/87, an inventor had filed a UK patent application and assigned it to a research council. The research council subsequently assigned the application back to the inventor, but only the research council and not the inventor had signed the agreement. The inventor then filed a European application claiming priority from the original UK application. The question was whether the inventor had also regained the right to claim priority, since the formal requirements under UK law for an assignment, namely that both parties to the agreement must sign, had not been completed. In this case, it was held that, under English law, the equitable title of the priority right had been transferred, even though the formal legal title had not. The priority claim was held valid on this basis.

In the UK, there has also been some respite provided by recent Court cases. The High Court case KCI Licensing Inc v Smith and Nephew plc ([2010] EWHC 1487; referred to herein a “KCI”) held that the right to claim priority had been transferred, both legally and in equity, by a confidentiality agreement between the inventor and KCI, completed between the filing of the priority application and of the subsequent application claiming priority. The confidentiality agreement included the wording:

I hereby assign and agree to assign to the Company all right, title and interest in all confidential information, inventions and improvements conceived or developed by me … during my employment and for a period of three (3) years after termination … I will communicate promptly to the Company all such inventions and improvements and will sign all documents reasonably requested by the Company to evidence the fact that such inventions and improvements are the sole and exclusive property of the Company …” (emphasis added).

As mentioned, the decision included a discussion of the Judge’s view that, even if this hadn’t been sufficient to transfer the legal title to the invention and to the right to claim priority from the original patent application, equitable transfer would have occurred. In reaching this conclusion, the EPO case J19/87, outlined above, was referred to. The KCI judgement was followed in a subsequent High Court case, HTC v Gemalto SA [2013] EWHC 1875 (Pat).

Furthermore, the more recent Court of Appeal case Idenix Pharmaceuticals Inc v Gilead Sciences Inc ([2016] EWCA Civ 1089; referred to herein as “Gilead”) cited KCI when determining whether the right to claim priority had effectively been transferred. In Gilead, the invention was made by the inventor in the course of his employment in USA by a party “PG”. The priority application was a US application filed in the name of the inventor and it was agreed that the wording of the inventor’s employment contract was sufficient to transfer the rights in the invention to PG.

However, the applicant for the priority-claiming application was a company referred to here as “PB”. The question was whether, when the priority claim was made, PB was the inventor’s successor in title.

PG was a wholly owned subsidiary of PB. When the companies were incorporated, it was intended that PB would engage PG to undertake research and development in the USA. PB would own any intellectual property that was developed by PG, for tax reasons. An R&D Agreement to this effect was drawn up, referring to the intention that “PB shall at all times … be the sole owner of all rights relating to or emanating from Intellectual Property, Know How, Improvements, or other matters developed in, or related to, a Project” (emphasis added).

The Court of Appeal upheld the first instance judgement that this was effective to transfer the legal title to the invention and associated rights to PB. However, it was also confirmed that, even if legal title had not been transferred, equitable title had been transferred and that this would have been sufficient to enable PB validly to claim priority under the provisions of the Paris Convention.

Because it is a Court of Appeal decision, Gilead now binds lower courts to apply the same approach when considering whether priority may be claimed, unless they can distinguish the fact pattern in order to reach a different conclusion. Indeed, the very recent case Fujifilm & Others v Abbvie [2017] EWHC 395 (Pat) confirmed that, provided equitable interest in the title of the priority right has been transferred, according to the evidence available, it does not matter if legal title had not also been transferred.

So, it seems that at least some EPO Boards of Appeal, as well as the English Courts, have stepped back from the insistence in T62/05 that a formal assignment document, mentioning the priority application by number and including reference to transfer of priority rights, is necessary for the right to claim priority to have been transferred. The claiming party need only have equitable title to this right.

However, it is hard to see how this line of case law would have rescued the priority claim in the Edwards case discussed above. In that case, the issue was that two of the inventors did not have an existing legal relationship with the priority-claiming applicant. In the absence of even some kind of confidentiality agreement or research contract, providing for the inventors to “hereby assign and agree to assign” the rights relating to the invention and to the priority application, it seems that even equitable transfer may not have taken place. In the KCI and Gilead cases, there was only a single inventor, so the issue did not arise.

Furthermore, the question of whether equitable title has been transferred is determined according to the law of the country in which the transaction resulting in the transfer has occurred. This transaction may be due to employment, or some other agreement. The question of whether or not equitable title has been transferred will be determined in accordance with the evidence, assessed according to the law of the relevant country. For example, in Fujifilm v Abbvie mentioned above, the Judge heard from experts in both US and German law. The provisions which apply may, therefore, be quite different than the law with which the primary legal advisor is familiar, for example if multiple inventors in different jurisdictions are involved.

It is also important to note that EPO case law is not formally binding on other EPO Boards of Appeal, unless there is an Enlarged Board of Appeal decision. Therefore, an unlucky party might find itself unable to succeed on the argument that there has been a transfer of the equitable right to claim priority, if facing a Board of Appeal which choses to take the more conservative approach.

In addition, the Fujifilm v Abbvie UK decision also indicates that, if equitable title has been transferred, an attempt by a party which still holds the formal legal title to claim priority may not be valid. This provides a potential different line of attack for a party seeking to establish that a claim to priority has not validly been made.

Great care should, therefore, still be taken when identifying the parties to be named as an applicant at the priority-claiming stage. The best advice remains to ensure that a formal assignment document is completed by the parties in the period between filing the priority application and filing the priority-claiming application, ideally shortly after the priority application has been filed. This would provide certainty that both equitable and legal title are held by the same party. If such a document cannot be signed in time, great care should be taken in assessing whether equitable title in the right to claim priority might already have been transferred, in order to identify the correct party or parties which have the right to claim priority.

The subject matter to be claimed

What can priority be claimed for?

Article 87 of the European Patent Convention, which puts Article 4 of the Paris Convention into effect, indicates that: “Any person who has filed … an application for a patent … or his successor in title, shall enjoy, for the purpose of filing a European patent application in respect of the same invention, a right of priority …” (emphasis added). The equivalent section of the UK Patents Act (Section 5(1)) refers to “… an invention to which an application for a patent relates …” (emphasis added). Therefore, these provisions allow an application to claim priority from an earlier priority application, provided that the priority-claiming application relates to “the same invention” as was disclosed in the priority application.

The “same invention” test is a strict one under EPO practice. The well-established EPO Enlarged Board of Appeal (EBA) decision G2/98 states that only subject-matter which a skilled person might directly and unambiguously derive from the disclosure of the priority application can be considered to be the “same invention” as the priority application. This mirrors the test used by the European Patent Office (EPO) in assessing added subject-matter. At least very strong implicit, ideally literal, basis for a claimed combination of features is thus required in the priority document in order for a priority claim to be valid for that combination.

“Same invention” at the EPO

This strict approach to the validity of a claim to priority means that claims which have been amended, introduced or broadened in a later priority-claiming application often have the filing date of the later application as an effective date. As discussed in the decision G2/98, this may lead to a loss of entitlement to priority in the following situations:

  1. The priority application disclosed feature A but the later application claims “A and B”. Since the combination “A and B” was not disclosed in the priority application, the claim in the later application is not entitled to claim priority.
  1. The priority application disclosed feature “A” but the later application claims “A or B”. In this case, the part of the claim covering “A” is entitled to claim priority, whilst the part of the claim covering “B” is not, instead taking the filing date of the later application as its priority date. The claim has more than one priority date, i.e., it has “partial priority”.

There are some situations where an “OR” claim is not presented in as clear a format as described in (2) above, but rather covers broader alternatives in a generic fashion. For example, this might be achieved by broadening a claimed range, or by broadening the definition of a class of chemical compounds. Such a so-called “generic ‘OR’ claim” was also confirmed in G2/98 as being capable of having multiple priority dates, “… provided that [the generic term] gives rise to the claiming of a limited number of clearly defined alternative subject-matters” (G2/98, paragraph 6.7 of the Reasons for the Decision).

 “Poisonous priority” at the EPO

Over the years, some arguments began to arise in cases at the EPO regarding the language “limited number of clearly defined alternative subject matters” cited above. Attacking parties (and sometimes Examiners) began to argue that, in a generic OR claim, lacking some explicit delineation of the priority-entitled subject matter and the subject matter not entitled to priority, there is no such “clearly defined alternative subject matters” and so the claim to priority must fail. For example, a priority document may disclose a range “3-5” and the priority-claiming application may claim a range “1-8”. According to this line of argument, this broader range would not be entitled to claim priority unless the range “1-8” were expressed in the claim as “1-2 or 3-5 or 6-8”. The range “3-5” is entitled to priority whilst the surrounding ranges are not.

Even more alarmingly for applicants and practitioners alike, this interpretation could result in an outcome where pairs or groups of published European patent applications, derived from and including subject-matter from a common priority application, could become citable as prior art against each other.

An example of such a scenario occurred in EPO Appeal case T1496/11, related to a self-verifying bank note which could be folded, twisted or bent in such a way that a lens located in a transparent section of the note could be used to view a security feature elsewhere on the note which would only be observable when the lens was in the correct position.

The priority application had disclosed the security feature as including a “printed or embossed feature”. However, the mention of “printed or embossed feature” was not included in the claims of the later priority-claiming application, so that the claims of the later application were broader than the claims of the priority document. Conceptually, the claim covered (a) a bank note which included the printed or embossed feature, OR (b) a bank note which did not include the feature, but the claim did not make such explicit description of “(a) or (b)”. Therefore, it was considered to be a “generic ‘OR’ claim’ which did not fulfil the requirement of claiming a limited number of clearly defined alternative subject matters. As a result, the application was found not to be entitled to claim the priority date.

A divisional application had been filed, the text of which was, as is usual, identical to the parent (priority-claiming) application which was the subject of the appeal in T1496/11. This divisional application was published and included the disclosure, in the examples, of the specific embodiment of the bank note being foldable upon itself so that a lens could be used to view the security feature, which was an area of microprinting. This embodiment was entitled to the priority date, because it corresponded to what was in the priority application. Since the claim to priority was disallowed for the parent application claim, the divisional application became prior art for novelty purposes (under the provisions of Article 54(3) EPC). Since the specific embodiment fell within the broader claims of the parent application, this caused the generic claim of the parent to be anticipated and, therefore, invalid.

Importantly, this scenario could play out in either direction, with a parent application acting as prior art against a divisional or a divisional application acting as prior art against a parent. The outcome depended on the scope of the claims as compared to the overall disclosure in the published text of the other application(s) in the family. It is common patent prosecution strategy for a parent to be allowed to grant with narrow claims in order to get an enforceable right granted, with broader claims pursued in a divisional application. Under the “poisonous priority” scenario, if those broader claims were not entitled to the priority claim, the publication of the parent application, including disclosure of narrow embodiments, might invalidate the claims of the divisional application and make it impossible to achieve grant of the broader claims.

G1/15 – EPO’s Enlarged Board of Appeal to the rescue

There was other EPO case law which did not agree with the approach used in T1496/11. Again, it was imagined that there may be a broad claim and a priority document disclosing a narrow embodiment falling within the claim. However, in these cases it was concluded that the broad claim is, therefore, made up of subject matter which is entitled to priority, along with subject matter which, although not entitled to priority, is novel over the priority disclosure. Therefore, the claim as a whole is valid, since its parts are either novel, or are entitled to priority.

Where there are two or more lines of divergent case law, a Board of Appeal facing a legal question may make a referral to the EBA for determination of the correct legal interpretation. The Board of Appeal in case T557/13 did just that, referring some questions to the EBA and asking them to clarify the correct approach.

The EBA concluded that the question to be answered, when assessing a priority claim, is whether the claim encompasses subject matter which is directly and unambiguously derivable from the subject matter disclosed in the priority application. If it does, the claim is entitled to claim priority, albeit for only a partial portion of the claim. To quote the EBA in G1/15:

6.4       In assessing whether a subject-matter within a generic “OR” claim may enjoy partial priority, the first step is to determine the subject-matter disclosed in the priority document that is relevant, i.e., relevant in respect of prior art disclosed in the priority interval. This is to be done in accordance with the disclosure test laid down in the conclusion of G2/98 and on the basis of explanations put forward by the applicant or patent proprietor to support his claim to priority, in order to show what the skilled person would have been able to derive from the priority document. The next step is to examine whether this subject-matter is encompassed by the claim of the application or patent claiming said priority. If the answer is yes, the claim is de facto conceptually divided into two parts, the first corresponding to the invention disclosed directly and unambiguously in the priority document, the second being the remaining part of the subsequent generic “OR” claim not enjoying this priority …”

The EBA observed that, although the exercise of determining what is directly and unambiguously derivable from a priority document may be a demanding one in some cases, it is a task commonly carried out by EPO Examiners and applicants. Therefore, there should be no difficulty to do so when assessing whether a claim has partial priority and additional tests or steps are not necessary.

Therefore, so far as the EPO is concerned, the concept of “poisonous priority” appears to be dead.

No more poisonous priority?

Not so fast. Unfortunately, there is also national law establishing the principle of poisonous priority, so a European patent granted by the EPO might subsequently come under attack in one or more national courts.

In the UK, there have been at least two cases where this issue has been relevant.

The case of Nestec S.A., Nestlé Nespresso S.A. et al. v. Dualit et al. [2013] EWHC 923 (Pat) (“Nestec”), concerned kitchen coffee machines such as Nestec’s Nespresso® machine.

Nestec’s original priority application disclosed a housing to receive a coffee-containing capsule, the housing being contained in a “moveable part” of the machine. By the time the later priority-claiming application was prepared, the housing was claimed as being (i) contained in the moveable part, or (ii) contained in a fixed part, or (iii) divided between the moveable and fixed parts.

The Judge found that the presence of part (iii) in the claim meant that there was no “clearly defined alternative subject matter” available in the claim, so in this case it was not possible to allocate different priority dates to different parts of the claim, as suggested in G2/98. Therefore, the whole claim was not entitled to the priority date.

The priority application was a European application which had been allowed to continue through the application process and was eventually published. Therefore, it was relevant as prior art for the novelty of the claims of the patent (under Section 2(3) of the UK Patents Act), as a result of the invalidity of the priority claim. Of course, the description of the priority application disclosed the narrow embodiment of the capsule being contained in the moveable part. This narrower embodiment anticipated the broader definition provided in the later application, so the claim overall was held to lack novelty.

Furthermore, a recent case from September 2016 (before the EPO decision in G1/15 was issued) has followed a similar line of argument. In Nicocigs v. Fontem Holdings & Fontem Ventures [2016] EWHC 2161 (Pat) (“Fontem”), the patent was found invalid at least because the scope of the granted claims was broader than the disclosure of the application as filed, as the result of amendments made during prosecution. However, the question of the relationship between the disclosure of the priority application and the validity of the claim to priority was also considered.

In this case, there were two parallel European patent applications, each claiming priority from the same, single, Chinese utility model. One of the European applications (referred to as “the ‘349 application”) was granted and came into force in the UK and it was this patent which was litigated in the UK Court. Both the ‘349 application and the other application (known as “the ‘350 application”) had been published on the same date.

The ‘349 application which resulted in the UK patent differed in various ways from the disclosure of the priority document, whereas the ‘350 application was identical in all material respects to the priority document.

The patent related to an electronic cigarette design. It was found that the priority document disclosed a three-part device comprising a battery assembly joined to an atomiser assembly, these two parts being contained in a shell, with a cigarette bottle assembly inserted into one end of the atomiser assembly. The patent, however, related to a two-part device having a shell containing a battery assembly and an atomiser assembly, the shell having a detachable end which further contained the cigarette bottle assembly. It was found that no such device was disclosed in the priority document. The patent was, therefore, broader than the priority document disclosure (which was also the disclosure of the published ‘350 application).

The ‘350 application was found by the Judge to provide an enabling disclosure of an embodiment falling within the scope of claim 1 of the ‘349 application. The patentee argued that, therefore, the ‘349 application must be entitled to a claim priority from the priority application, since it was identical to the ‘350 application. Against this, the claimant argued that, for priority to be claimed, the priority disclosure must support the claim across the whole breadth; because this was not the case, the claim was not entitled to claim priority. According to this argument, there could be no partial priority for the claim. The Judge agreed, therefore concluding that the ‘350 publication (which was entitled to claim priority), was part of the prior art for novelty and that the claim lacked novelty in view of it.

This outcome was partly the result of the patentee’s preferred interpretation of the claims, which they had argued should be construed so that the claimants’ product would infringe the patent claims, if valid. A different conclusion may well have been reached had the claims been construed more narrowly. Indeed, in the High Court decision Unwired Planet International Ltd v. Huawei Technology Co. Ltd and others ([2017] EWHC Civ 266)  it was noted that “The exercise in determining priority involves asking whether the invention is directly and unambiguously derivable from the priority document, not whether every possible embedment of the invention is so derivable”. However, until there are further decisions in the UK which confirm agreement with the conclusions of the EBA in G1/15, it may still be possible to argue in favour of “poisonous priority” in the UK.

Although the UK Courts often follow EPO Enlarged Board decisions, in view of the Nestec and Fontem cases described above, patent applicants and legal practitioners should remain cautious with the content of a priority application and its interaction with any family members which may claim priority from it. We await an English Court of Appeal decision to clarify the question of “poisonous priority” in the UK and, specifically, whether the decision of G1/15 is to be followed by UK Courts.

Furthermore, with Europe’s new Unified Patent Court due to start work towards the end of 2017 or early 2018, it should be remembered that there is, as yet, no case law at all for that new Court. It is to be expected that decisions of the EPO Enlarged Board would be highly persuasive, but the European Patent Convention is only one of the sources of law for the new Court, another source being the national law of member countries. Therefore, the judges in the Unified Patent Court might be persuaded by either source of case law.


Despite being a principle established for almost 135 years, the ability to validly claim priority can be more complicated than it first seems, as reflected in the cases discussed here. Practitioners should exercise the priority right with care.

On the question of the party entitled to claim priority, the European Patent Office and English courts have clarified the possibility of relying on an equitable transfer of the right to claim priority, even if a legal assignment document has not been completed. A written agreement before priority is claimed is still preferable, however, as care is still required if a priority-claiming party intends to rely on an equitable transfer of the right to claim priority. Indeed, it is possible that some Boards of Appeal may still prefer to decide on the basis of the stricter interpretation of the law.

On the question of whether an application or patent claims priority for the “same invention” and whether or not cases derived from the same priority application can become prior art against one another, this is now settled favourably for applicants, so far as the European Patent Office is concerned. However, national courts and the new Unitary Patent Court may take a different view.

Therefore, the content of the priority application remains crucial. Although additional data might be used to support the disclosure when the priority-claiming application is filed, alteration of the scope of the definition of the invention should be handled with care, particularly if the alteration represents a broadening in scope. This often requires extensive planning ahead at the priority filing stage. In some cases, it may be preferable to seek the advice of a European adviser during the preparation of a priority-claiming application.

If broadening is necessary or warranted by the additional work of the inventors, care should be taken to ensure that the various embodiments which might be entitled to different priority dates are clearly specified as alternatives, even if the main claim is initially presented as a generic definition. This allows flexibility when claims are amended during prosecution. Features which might be required for use as a disclaimer should be stated as such in the text, where possible.

Careful management of an application portfolio should include consideration of whether to allow a priority application to be published, whether to file multiple applications claiming priority from the same priority application, and whether and how to use divisional applications. Ideally, you should keep your European representative informed from an early stage in the application management process.

This update is for general information and does not constitute legal advice. If you have any questions regarding the issues discussed in this update, please contact your usual Greaves Brewster attorney, or Rhiannon Turner.