Trolle,
I have similar qualifications to you. Am about to sit for my last 6 exams next week.
I highly recommend, as someone earlier did. Go to the CAA website and look at the LASORS publication. Or buy one. It used to be £10 and they ship it to the US, that is what I did and it cleared all my questions.
You need to do the papers first. If you, like me have done most of your flying in the States, I suggest maybe doing your commercial at an approved school in the US. As for the IR, the test has to be done in a JAA country, hence what the US schools do is train you in the US and then you come to e.g. England to do the check-ride. Often that tends to be too much of a transition, due to differences in airspace etc.
Here is what I did and plan on doing.
Dist learning - £2700
Comercial in the US £1500
IR in the UK £5000
MCC £2800
That is my realistic budget including exams etc. Though I have given a bit extra for the IR, since I believe the first time pass rate in the UK is near 30% now.
If you have any more questions PM me. But be patient, I have exams next week.
Good Luck
Speed