Sorry about the shoddy pics - they were about 8 metres up a tre and it was blowing a hooley... They look like they might be Dunnock to me but also seem a bit different to others that I've taken that are much more clearly Dunnock.
Siskins are a pretty small bird and slender in the body. The top 2 birds seem quite rounded, and look nothing like the Siskins I have been watching this afternoon in my garden. I suppose if they are huddled up while feeding they will look a more rounded bird.