The Serpentines' running club is very good (huge) and a massive selection of different training runs at diff times of the week. They do hill training at Greenwich on Saturdays (which is great), also club runs in Green / Hyde Park (again Saturdays), and long runs in Richmond at the weekend. Many runs and other sessions each night of the week. Their home is the Seymour centre in central London. I know it's not Deptford, but it is a great club.
More info http://www.serpentine.org.uk/ and there are lots of se london folk in it.