This chapter primarily deals with double patenting arising from the filing of a divisional application, but also treats the matter as it may arise in other procedural situations. The leading decisions on the issue are G 1/05 date: 2007-06-28 (OJ 2008, 271) and G 1/06 (OJ 2008, 307), in which the Enlarged Board held that the principle of the prohibition on double patenting was based on the idea that the applicant had no legitimate interest in proceedings that gave rise to the grant of a second patent in respect of the same subject-matter for which he already held a patent, see in this chapter II.F.5.1. In T 318/14 questions concerning the prohibition of double patenting were once again referred to the Enlarged Board of Appeal (see below).
The technical boards have several times considered the notion of the "same subject-matter". A mere (partial) overlap does not prejudice the grant of a patent (see T 587/98, OJ 2000, 497; T 877/06; T 1491/06; T 1391/07; T 2402/10; T 2461/10; T 1780/12; T 621/15). See in this chapter II.F.5.2. On the relevance of the scope of protection for the issue of double patenting, see e.g. T 1780/12 and T 2563/11.
Some technical boards have sought to identify the legal basis for this prohibition in the EPC and have suggested Art. 125 EPC (see T 2461/10 highlighting that the "legitimate interest" was a general procedural requirement – see T 9/00, OJ 2002, 275 – and one of the principles of procedural law generally recognised in the contracting states; see also T 2563/11 agreeing with T 2461/10 that this is in line with the travaux préparatoires; but see also T 307/03, OJ 2009, 422 and T 1423/07), or Art. 60 EPC (T 307/03; but see also T 1423/07 and T 2461/10). As noted in T 2461/10, the EPC only contains a provision relevant to the prohibition on double patenting in the context of European and national applications and patents (see Art. 139(3) EPC). Some of these decisions are summarised in this chapter II.F.5.2.
On the matter of double patenting arising not from the filing of a divisional application but from internal priority the board in T 1423/07 held that double patenting was not prohibited for European applications claiming a European priority because of the applicant's clear legitimate interest in the longer term of protection possibly available with the later filing, in view of the fact that the filing date and not the priority date was the relevant date for calculating the 20-year term of the patent. In T 2461/10, however, the board noted that double patenting could arise in three scenarios: two applications filed by the same applicant on the same day; parent and divisional application; and a (European) priority application and a subsequent (European) application claiming this priority. The board concluded from the travaux préparatoires that prohibition of double patenting applied to all three scenarios. It also highlighted that G 1/05 date: 2007-06-28 (OJ 2008, 271) and G 1/06 (OJ 2008, 307) had referred to a legitimate interest. With reference to the travaux préparatoires the board doubted that the interest identified in T 1423/07 could be considered legitimate. In the case at issue, the board could leave the question open, as there was no identity of subject-matter but merely an overlap of scope of protection.
In T 318/14 the board referred the following points of law to the Enlarged Board of Appeal in accordance with Art. 112(1)(a) EPC:
1. Can a European patent application be refused under Art. 97(2) EPC if it claims the same subject-matter as a European patent granted to the same applicant which does not form part of the state of the art pursuant to Art. 54(2) and (3) EPC?
2.1 If the answer to the first question is yes, what are the conditions for such a refusal and are different conditions to be applied where the European patent application under examination was filed
a) on the same date as, or
b) as a European divisional application (Art. 76(1) EPC) in respect of, or
c) claiming the priority (Art. 88 EPC) in respect of
a European patent application on the basis of which a European patent was granted to the same applicant?
2.2 In particular, in the latter case, does an applicant have a legitimate interest in the grant of the (subsequent) European patent application in view of the fact that the filing date and not the priority date is the relevant date for calculating the term of the European patent under Art. 63(1) EPC?