Firstly be more specific,
For your first multi crew type you need a valid and current Single Pilot ME IR.
For additional / further multi crew type ratings it use to be the case that there was no requirement to hold a current IR (I know I completed my second type rating on the grounds of a previous multi crew rating with neither my MPA or SPA IR current). That however was under JAA rules according to that listed in LASORS. I haven't checked CAP 804 to see if the same applies under EASA.