Krallu
If you want to fly IFR only in the UK, the IMC Rating is pretty good for that. I fly a non-known-ice aircraft and find that whenever I can't fly it is either because of 0C (actual or forecast) below the MSA, or cloud (actual or forecast) below the MSA and no IAP at the destination.
A full IR would give me airways capability but that's of little use for safely beating icing conditions unless you can get a reliable forecast for the cloud tops - which you can't.
For Europe, the full IR is more or less essential for pre-planned flights throughout the year.
So I think that for the UK an IR has little advantage over the IMCR unless you have a known ice aircraft with a turbo. One of those (new) is some £270k+VAT minimum, e.g. a TB21 with full TKS.
A known ice turboprop is even better, of course
The serious business flyers who can't afford a jet (or don't want an aircraft which is of no use outside the airways) tend to go for those.
I take it you know about the FAA PPL/IR / N-reg route. But from your last question, probably not.