IMC Rating is UK airspace only. It's easy enough to get though. You also can't go into Class A airspace (which isn't a real issue in the UK, at the level of aircraft type which a PPL is likely to be flying) and you need 1800m visibility for takeoff and landing (which isn't a problem either; it's really only fog that goes below that).
The full
JAA (European) Instrument Rating is rather more than 7 exams. The ATPL version is 14 exams; the PPL/IR is (I think) about 10 but some have been combined into a single sitting. The study material is 3-4
feet of paper thickness; I've seen it. It's a truly massive undertaking in terms of a chunk of life dedicated to it and the required feat of memory, which almost nobody does unless they want to fly commercially. There are also additional medical requirements even for just a PPL. Flying is 50hrs min for single and 55hrs min for multi engine IR and that is probably the easiest part! The IMC Rating training does not count towards the flying requirement but there is a committee working on that right now and it appears this (together with a approx 20% ground school reduction) will be one of the changes.
The
FAA (American) PPL/IR route is the popular option for
private flying with an IR. The FAA IR study material is about 2" thick and can be done in say 6 months if you also have to work and have a life. But to get worldwide privileges you need an FAA registered aircraft, which tends to imply buying one (lots of $$$). Existing ICAO (i.e. done almost anywhere in the world) instrument training counts towards the FAA IR requirements.
Whichever way you look at it, if you want to fly in a way that needs an IR, you will find it hard to rent a plane that's good enough, so your budget needs to be that much bigger. The school may not put it quite like that though
If you have the budget to pull this all off, consider doing an
FAA PPL only initially. You can fly a G-reg plane on it, worldwide, VFR. You get an FAA medical (plenty of UK based doctors). Then, you can add the FAA IR to it. The UK CAA or the UK flight training scene are not involved at all; in fact due to recent restrictions you will
have to go to the USA for the PPL. UK PPL training will count fully towards the FAA PPL training requirements (aren't the Yanks generous; you can't do this the other way round).