The IMC is valid for 25months each time, and once on your licence, can be revalidated automatically by the examiner each time you do an IR test.
This no longer applies to holders of multi-pilot IR(A)s, thanks to the CAA.
When I asked them "Why did it change", they mumbled something about "Limited panel UPs are not tested during a multi-pilot IR test".
"And how about the UK ATPL(A) holder who
never needs to revalidate an IMC rating?".
"Ahh....errrm, err, well.....hmmm.....nice weather today, isn't it?"
In other words, an ill thought-out change which hadn't even been subjected to industry consultation, let alone a regulatory impact assessment, being a change to national law.........