I have just completed the FAA unrestricted ME/CPL/IR at Orlando Flight Training in Florida. I can recommend them, the instructors work very hard at getting you through. You do have to demonstrate a higher standard than for a UK IMC rating. I had to fly back course ILS, DME arcs and quite a bit of NDB. I am told the check ride is every bit has hard as the UK IR check ride and. You can do the flight training at a UK FAA approved school such as Solo Flight at Humberside airport. However the check ride has to be with an FAA examiner. I am told there is one in Germany, otherwise you would have to go to the states. You can take the FAA IR ground exams here in the UK. The King Video Course is great at getting you through with a high score.You still need to pass an oral exam before the check ride and that is the hard part, my oral exam lasted three hours. I am told many don't even get to the aircraft as they will fail you if you don't know you subect inside out. Once you have the ticket you do need to keep current. Have a look at the FAA FAR/AIM for all of the rules and requirements.
Good luck.