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.
Can an FAA IR be maintained(revalidated) by experience?
In which case I may have been confusing:
Test vs LPC
with
Test/LPC vs Revalidation