you can fly in the UK on your FAA licence. Contact a club and get a check out. You may not use your night priveledge in a G registered aircraft.
Tucked away in LASORS (the CAA version of the FAR/AIM) Section B B1.1 Annex 1, you will find a paragraph with regards to your radio licence and it states that you need to contact the FCC to get a paper copy of your radio operators licence before you can operate any radio station. i.e. without this you are not operating an aircraft illegaly, but you are operating a radio illegaly (unless accompanied by a pilot with an RT licence).
This can be obtained from here wireless.fcc.gov/uls and believe it or not, there will be a "small" admin fee of aprox £75
On a side note, I wonder how few people have actually done this?
basically. go and have a checkride and enjoy flying here.