The CAA will issue an IMC/IR(R) on the basis of a foreign ICAO IR valid for 25 months from the date of the last IR Test - They do not recognize an FAA Instrument Proficiency Check as an IR Test so this would be useless (on its own) for obtaining or maintaining an IMC Rating.
Incorrect I am afraid. I have held an FAA IR since 2002 and also an IMC /IR(R) since the same time. I always re-validate the IR(R) by sending evidence of the IPC to them (logbook and endorsement), filling in the CAA form and paying the fee for the issue of the rating.