Sean,
Ignore all references to an "IMC" rating. This is a local UK rating not recognised anywhere else in the world.
What you want to do is obtain an Instrument Rating.
In order to obtain an instrument rating, you must basically;
a) Complete certain Ground exams laid down by the relevant authority
b) Demonstrate certain medical standards with respect to hearing
c) Complete training
d) Pass a flight test
Considering your situation, I think that you need to complete a) and b) above before traveling to Europe.
In advance, you must also check out as many training providers as possible and make sure you are getting value for money based on what training your national authority requires.
Prior to commencing training in Europe, you must obtain a letter from your national aviation authority approving your intentions to train at a certain school covering a certain sylabus and completing a flight test at the end using a European examminer or completing a flight test on return home.
Overall, the important thing is to have everything in writing so that you do not spend a small fortune in Europe training only to finad that you require to spend another large fortune at home meeting local requirements.
Make sure that the amount charged by a UK school is the same as charged to local pilots completing local courses....they do love to charge extra...example JAA IR course (55 hours) £12,000. 15 Hours twin IR training.......£8,500......work that one out!!!
Finally if you are based in London then do not forget that France is close at hand and mostly operates on a non-profit basis for training while Ireland is also close at hand an offers training at cheaper rates due to the lower costs of may operators some of which are also operating on a non-profit basis and thanks to the Euro, prices across Europe except the UK can be compared.
Regards,
DFC