You actually need to read on a little further in JAR-FCL 1. Appendix 1 to JAR–FCL 1.205, which deals with the modular IR(A) course, states:
"An applicant for a modular IR(A) course shall be the holder of a PPL(A) or a CPL(A), either licence to include the privileges to fly by night, issued in accordance with ICAO Annex 1. The Training Organisation shall ensure that the applicant for a multi-engine IR(A) course who has not held a multiengine aeroplane class or type rating has received the multi-engine training specified in JAR-FCL 1.261(b)(2) prior to commencing the [flight training for] IR(A) course."
This allows the holder of a non-JAA licence to undertake the IR(A) course prior to having a JAA licence issued. However, if you hold a JAA licence, the requirement for that licence to include the privilege to fly by night can only be fulfilled by the JAA night qualification. Therefore, no JAA FTO should accept you for training unless your PPL includes the privilege to fly by night and the CAA may well refuse to issue the rating unless you hold a JAA night qualification.