CM and bookworm have it spot on, as usual. There are plenty of IFR-equipped aircraft in groups around the UK - I'm in a group of 6 on an "airways" Arrow at Southend, and we aren't the only IFR group there.
If you're looking to join a group once you have your PPL, I'd suggest do the night rating and IMC rating before you look for a group. An IFR group aircraft is likely also to be a "complex" type (not always, but many are) and the insurers and group members might not be too keen on a low-hours PPL with no added ratings. Not impossible, but might not be easy, depending on where you are.
Ours is a group of six, and you'd need £10k and £100 a month to join, then £65 an hour to fly. Plus occasional "top-ups" to the funds when FM-immune or Mode S or whatever brings an unexpected bill.