In a nutshell, GA is generally more expensive over in the UK, but is not prohibitive depending on what the $ is doing, and how rich you feel. I've been living in the US for too many years now to be completely in touch with the UK scene, so I've chosen to point you in the right direction in my notes below:
Many Brits come across here to the UK to do their private certificates, and then return and get checked out at their local airfields. Unless there has been a change in the rules (implementation of JAR etc.) I believe you can do that too with your FAA cert. I know that the FAA issues about 2500 Temporary Certificates to UK license holders each year and I think it works the other way too. Finally on the license issue, check out the CAA Civil Aviation Authority website (the Brits equivalent of the FAA) for more info at:
CAA
For good information on where to go, where to fly etc., check out Flyer magazines website:
Flyer Magazine which has a great directory of schools and places to rent aircraft across the UK by county and a whole bunch more.
For the most part you can get a briefing on airspace differences when you get there although you could glance at the
CAA Chart Site to see downloadable VFR charts which I think they have on trial at the moment.
In my day, Pooleys were the equivalent of Sporties, so you might try them for charts, flight guides etc.
Pooleys
Well, there you have it .... oh, and I nearly forgot, the weather can be atrocious. How can I forget that? My general advice to you is grab your license and medical, hit the Flying Mag website and choose a Flight School near to where you will be, and go and get checked out by a local instructor. If your'e heading for Scotland, make sure you visit a small tarmac strip at Plockton in the Western Isles...if you can make it there, the locals will look after you! I used to live there.
Finally, drive on the left....or better still, get someone else to drive.
PM me if you want advice on specific places to visit....enjoy.