NEVER go on whats in the SERPs. Get recommendations - so MOz is a good place to start.
Why not look for the really technical SEO posts on moz and then approach those companies? I can recommend Distilled
You could look at the http://moz.com/community/users users board and pick someone from London that has a ton of points - this indicates they have been helpful to the SEO community over a number of years. I'm at 21 and I am based in London. Marcus Miller is at 12 and he is based in Birmingham
There is also a MOZ recommended list http://moz.com/community/recommended
Stephen