Yo Apstyle!
'guya' seems to know his stuff ! maybe message him for some advice. Another poster I've seen here who knows alot is 'lizzit'.
I get a property magazine called 'A place in the Sun' and there's a sister publication called 'Everything America' and at the back of that there's listings of US/UK lawyers. Have a look through that or its website ( i think theres one) of course, do some yahoo'ing and 'googleying' as well, bound to turn up quite a few in London!
I know a little bit about UK/US tax but only to the basic level as I worked for Intuit and it's Quickbooks, Quicken, TurboTax and the UK equivalants and mainly as a IT/programming bias.
good luck!
Dennis! West London & Slough UK!