Don't forget, there's lots of other possibilities in and around London.A good starting point is the
CAA's list of Part 145 approval holders.
You'll need the list of codes for ratings used in that list; EASA being what it is that's buried deep in Regulation 2042/2003, as Appx IV to Annex I/Part M.
This is a link to the whole Regulation, p 68 is what you want. (The pages are not numbered, but the PDF reader provides a number. At least mine does!).