However the statement did arise ( form a respected CFI) that the CAA would grant an IMC rating on the basis of a FAA IR and was curious to know how it might work. I'll do a bit more digging !
This was the case back in the 80/90s before the introduction of JAR-FCL in 1999. It may have even extended beyond that date, but I have not come across any case of it occuring in the last 15 years.