Bermuda and Caymans accept FAA IR for all CAS, yes, and they also accept FAA certification (which is quite funny since
AFAIK one or both of these employ CAA inspectors to do it) but they also have a lower limit on aircraft size (around turboprop size) which makes them worthless for "us". Same for Aruba, which is basically Netherlands and thus probably within JAA.
Cathar - the money would be made by running a registry. You would get say £500/year from every small plane, and much more from the bizjets etc.
There wouldn't be any formal trade war, but it wouldn't take much to p*ss off the American
buyers of European (particularly French) products if UK or Europe took such action against US aircraft. The decision whether to buy a Boeing or an Airbus is a very finely balanced one. Look at the EADS adverts in the USA; they go to huge trouble to put an American face on the company, by putting up pictures of Americans running the U.S. bits of it. Anything to hide the fact it is a European, and virtually French-run, business. These are important dimensions. Why do you think the French withdrew their own proposal to kick out N-reg planes so rapidly, once the word got out?