West Coast,
The IMC is a very strange thing. It's incredibly expensive and complicated to get an ICAO IR in the UK, basically it's a "professional rating" whatever that is. So given the generally cloudy weather in the UK, the CAA have been very pragmatic and come up with an IMC. This is a 15 hour course (yes you read that right, fifteen) which lets you fly in the clouds and even shoot approaches in airspace where you will be unlikely to hit a real IR pilot.
This board is full of the repeating threads. I've seen multiple threads asking what the DH and RVR are when flying a Cat I ILS in Class D and all you have is an IMC. I don't think anybody has come up with an answer they could defend!!!! If you were flying that approach with an IR it would be an easy one. Some people argue that your DH or RVR can be lower flying with an IMC than if you had an IR!!! Confuses the hell out of me. Instead of making IR's accessible like in the US, the CAA makes IRs totally ridiculously hard to get, and fills the gap with this complicated beast called an "IMC"
So that is my understanding, happy to be corrected.