Just to add if anyone is looking for a good alterations service I used Friends of Fabric on Bellenden Road and they did a fantastic job with my dress. The price was extremely reasonable (after some very expensive quotes from other seamstresses!). I would highly recommend their service.
I'm looking for someone who can alter a dress for me, at a reasonable price; preferably based in the East Dulwich/Peckham area but I'm willing to travel a bit if anyone can recommend someone. Thanks a lot!