If a lack of unity is raised at the search stage for an EP application, a search is conducted for the invention first mentioned in the claims (see F‑V, 3.4) and the applicant is invited to pay additional search fees. Furthermore, the applicant is warned that, even if a further lack of unity "a posteriori" arises in the procedure, no further invitation to pay additional fees will be issued.

If the applicant pays any additional search fee, a search is carried out for the inventions for which those search fees have been paid.

If the search reveals that one or more of these inventions also lack unity "a posteriori", only the first invention of each of the groups of inventions is searched. No further invitation to pay further additional search fees is issued.

The search opinion is prepared, setting out the reasons for non-unity and giving an opinion on the patentability of the inventions paid for (see B‑XI, 5).

Inventions that have not been searched can be filed as divisional applications in accordance with C‑IX, 1.2.

A lack of unity objection is raised identifying four different inventions A, B, C, D. The first invention A is searched and the applicant is invited to pay further search fees for inventions B, C and D. The warning clause mentioned above is used.

The applicant pays two further search fees for inventions B and C. During the additional search, B is found to lack unity "a posteriori" and is divided into groups of inventions B1, B2 and B3.

In this case only B1 and C are searched. In the ESOP, full reasoning must be given as to why the claims of the application were divided into A, B, C and D and why B was further subdivided into B1, B2 and B3. In the ESOP an opinion on patentability must be given for A, B1 and C.

Examination of the application in the European phase will be based on either A, B1 or C (see C‑III, 3.1.2). The claims relating to inventions B2, B3 and D can be filed as divisional applications in accordance with C‑IX, 1.2.