This chapter deals with double patenting arising from the filing of a divisional application. The leading decisions on the issue are and G 1/06, OJ 2008, 271 and 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.
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), see in this chapter II.F.5.2.
Some technical boards have sought to identify the legal basis for this prohibition in the EPC and have suggested Art. 125 EPC (T 587/98, OJ 2000, 497; but see T 307/03, OJ 2009, 422), or Art. 60 EPC (T 307/03; but see T 1423/07). 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). These decisions are summarised in this chapter II.F.5.2.
For the matter of double patenting arising not from the filing of a divisional application but from internal priority see T 1423/07, in which the board 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 (see also T 2461/10, which also concerned a case of internal priority and which left this point open).