I have been told that as long as the UK license is current, the FAA one is also. Therefore as long as you do your SEP renewal every 2 years for your UK license, you are good to go. I have flown in the States (well California at least) and never been asked for a BFR.
I fly an N-reg and thus was concerned that, at SEP renewal time, I had to 2. One for the UK and 1 for the FAA. I know a lot of N-reg flyers working on this principle with FAA foreign license.
I hope I'm not wrong
I think it's one of those things that you get a different answer depending on who you ask.