Hello O Bojarski,
If I researched you right, you're from Atlanta originally, Possibly you want a fee-only planner in the USA sense, which requires the planner to take fees only directly from clients. Almost all IFAs in the UK accept money from life companies and banks, and indeed take their 2% - 3% charge from the investment of new money - so you'd exclude them. Then you also have another two constraints - a planner with UK and US tax competence.
Thun - mentioned in this thread - are not authorised in the UK as far as I can telll from the FCA register. I too admire their website, don't agree with some of their conclusions because (1) there's no point in analysing tax unless you also analyse charges and (2) their solutions oblige one to use a US broker who is not willing to place trades, for instance, in Hong Kong or Mumbai. They're a good firm, but it's difficult to see how you can get advice from them legally on European soil.
Without meaning to say this with overtones of pride, or self-importance, I think I am the only fee-only planner authorised by the FCA, understanding UK and US tax with the qualifications you want. There may be others. You can start to look on the CFP Board planner search - search for those in the UK, or London. Last time I looked there were three. Then you can go through the Chartered Inst. of Tax site for a tax qualified person also on the other list.
I'm happy to advise without pitching for asset management. You're welcome to contact me with a private message. I don't want to talk about our services here because forum members are good enough to give their time and know-how freely and I respect that and want to support this forum's culture.