If you have done your CPL/IR (frozen ATPL) and your IR has gone past its one year validity, you need not worry, so long as you have held a full procedural green in the last 5 years - link to LASORS Sect F here
http://www.caa.co.uk/docs/175/Sectio...LICOPTERS).pdf
Page 18 - Pre-requisites for training
The text reads:
"An applicant for the first type rating course for a MPA shall provide evidence that the following requirements have been met:-
b. hold a current and valid multi-engine instrument rating (aeroplanes). This is only a requirement for an initial MPA type rating and not subsequent type ratings. A UK QSP(A) who has held a Green Instrument Rating within the preceding 5 years is deemed to hold a 'current and valid' Instrument Rating".
Hope this helps.
GnP