Thanks for your help guys!
I eventually managed to get one of the training schools from America to call me back. I’ve been looking at a few in particular, one was call UK FT (UK Flight Training) and the other one was called Ormand Beach Aviation. They both seem to be reasonably priced and when UK FT called me back they cleared a few things up. They mentioned that the minimum requirements were 150 hours and a night rating, then you can go on to do the CPL/ATPL ground school but that it HAS to be done in the UK. You can also do it on a self study program from home as an online course over a year as opposed to doing it as a full time 5 month course. After you’ve completed ground school you then have to complete a CPL practical course which now includes the multi-engine rating.
Finally, you need to do the Instrument Rating which can be done over in America but in order for it to be upto JAA standards, it needs to be converted when you get back. I’ve asked them to email me some more info as what he told me on the phone was a bit baffling.