An American, writing stories that take place in London - that'sme.
I have gotten feedback on my previous effort that my vocabulary and syntax, although acceptably British, seem to have gotten trapped between the wars. Do you know any writers I might enjoy, who will simultaneously help me modernize my speech? I prefer cozies, but also read police procedurals. So called "soft-boiled" is OK, as is humor. (If you read American authors, my favorites are Laurie King - although I like the Kate Martinelli books much better than the Mary Russell ones - and Margaret Maron - Deborah Knott, rather than Sigrid Harald.) I just can't take truly violent crimes where you have to deal with the victim afterwards, or extended descriptions of cruelty and gore. I can read the news for that. So if there are authors you like who fit the bill, I'd love to know about them.
Please don't shoot me for this - but I'm going to say J.K. Rowling (writing as 'Robert Galbraith'). I enjoyed her last mystery novel, "the Cuckoo's Calling" enormously. It has the advantages of having a wide range of characters from various backgrounds, done by a writer with a good ear for dialogue, an interesting plot, and is set in London. Some found the story a bit slow and while that's true in some places, I still really liked it and I think it's an excellent writing example particularly if you want to get a feel for British characters.
Good Luck! I'm a non-Brit writing a story set in Britain as well, and although I did live there for a while, it's no easy task, but I don't see any reason not to attempt it :)
What's with this whole Americans-writing-British-mysteries thing (not that I am in a position to criticize)? Elizabeth George, GM Malliett, Deborah Crombie. All the British authors seem to be writing period fiction.
Mark Billingham - he straddles the police procedural/thriller/mystery genres and most of his novels are set in London (The Tom Thorne series). He also has a very easy, natural, 'British' writing style. Try 'Lifeless' or 'Death Message'.