JAR-FCL 1.250 - Type Rating, Multi Pilot - Conditions
(a) Pre-requisite for training: An applicant for the first type rating for a multi-pilot aeroplane type shall:
(1) have at least 100 hours as PIC of aeroplanes;
(2) have a valid multi-engine instrument rating (A).
(b) Training for additional multi-pilot type ratings require a valid multi-engine instrument rating.
From this it would appear you need the IR, but not the MEP Class rating.
Regards