Try Bristol gs. Fantastic bunch of people, got me through with no real troubles.
As far as I can remember, the ICAO IR has to be current for conversion as does the ICAO medical. Do the CPL in the UK, in UK airspace with UK RTF for what its worth. Forget some of the Florida factories.
There are some schools in Spain (one reasonably good one in Malaga) for the IR conversion. You will hear all sorts of stories on this no doubt, but it has worked for many I know on a (relative) budget. If one has a foreign MEP rating there should be no need to do a JAA MEP class rating before the IRT. The examiner will be able to test for both the IR-SPA-MEP and the MEP ratings together in most cases for a conversion case.
The CPL(A) will be training as required. For the IR it's 15 hours of which 5 have to be in the aircraft, the rest in the sim. This is feasable ONLY if you have flown in Europe before. Know the place and procedures well. The 5 hours on the aircraft route will only work for people with a modicum of time in the book, not 300 hour 'wonders'. For those that have not yet completed an ICAO IR to convert - DO NOT skimp on the foreign training!
Another thing, if you have more than 500 hours multi crew then get a letter from the foreign employer to verify this for an exemption from the MCC.
I speak as an ex JAA school Chief Flying Instructor and both JAA and FAA and DCA licence holder.
All the best, im off to fly my jet on my FAA licence...