Speaking to another guy yesterday who has a similar license and he said that the MPA IR carries across as an IMC rating regardless, asked our CFI who also thought this was the case.
That was indeed
once the case, but
without any consultation, the CAA ended this privilege at least 6 years ago - except, that is, for UK national professional aeroplane licence holders at CAA or ATPL level, who have embedded IMC privileges.
I was on the point of raising an objection to this high-handed Belgranist behaviour, but then one of my FIs (a ba 767 captain) went and failed his IMC test with a CAA examiner in one of the rear seats.....