There is an accurate piece of text in Lasors that describes this. Section F:
Many TRTO's dont seem to know this, and blindly insist that you go out and waste a grand or more revalidating an IR which is not needed.
Pre-requisite conditions for training
An applicant for the first type rating course for a MPA shall
provide evidence that the following requirements have
been met:-
a. have completed at least 70 hours as pilot-incommand
of aeroplanes;
b. hold a current and valid multi-engine Instrument
Rating (Aeroplanes). This requirement applies to a
first MPA type rating.
For subsequent type ratings
the Instrument Rating may be renewed if necessary
during the type rating course and skill test.