It will all be in Lasors.
AIRC you get 5 hours off for a CPL but nothing for an IMC.
Remember the IR is a JAR qualification and the IMC is a regional (CAA) anomoly.
If you do a FAA IR you can do the 15 hour conversion (although you will probably need more).
Basically, if you want an IR go and get one. If all you want to do is fly IMC in the UK an IMC will provide the legal mechanism to do it.