Your best bet might be those mobile scratch removers, do a Google search. There are a few garages in SE1 (I use Millenium garages, which is the closest but not cheap) and there are a few others but most don't open at the weekend.
SE1 Bodywork, 171 Abbey Street, SE1 3GR; 020 7231 3061 recently did a good respray job for me on my Audi TT. It's a one-man band and the premises don't look that much, but the guy is very friendly and helpful and I thought the work was good value for money. He is in the railway arch (south side) on the right just past the Tesco that is on the corner of Jamaica Road and Abbey Street. The first couple of arches are a garage called "General Autos" and then you come to "SE1 Bodywork". Definitely worth getting a quote.
I live on Long Lane SE1 and their was a spate of incidents where parked vehicle were damaged last week. I came online to search for a company to repair my wife's damaged Audi Q7 bodywork after it was scratched by a key or some other implement by a kind hearted individual ( putting it nicely !! )
I done some research online and found a wonderful company called Bumper Repairs at www.bumperrepairs.uk.com who provide a mobile car damage repair service in SE1. I called at 10am today and one of their technician fellows was with us at 11.30 and finished up about 20 mins ago with the vehicle looking amazing and back to how it should be.
Cant fault them at all, very professional and easy to use booking process and the repair chap that came was very knowledgeable and straightforward and he obtained a perfect match of our existing paintwork, so they definitely get a thumbs up from me.
I am not affiliated wth the company and am posting so that hopefully someone in need may find them useful.