I've just come across the following page - a goodhumoured look at getting around Britiain which seems also to be pretty accurate in what it says. Excellent notes of when you can drive on a USA license and when / how you get a UK one ...
http://prettygoodbritain.com/faq/a2b.htmlA post by sam, on another board within UK-Y, lead me to find this after a bit of browsing on what is - I'm 90% sure - his own web site; the hint was there in the other post, than name "Sam" keeps cropping up, and he puts walking and bykes first! Thanks, Sam - great contribution.