I'd concur with roz' suggestion that the NCT is still a good port of call. Forest Hill NCT is very large and active and as well as being a source of information about daytime activities aimed at parents with kids in tow, there are regular open houses and tea groups, mums' nights out and there is a regular evening book group.

We're also very lucky in Forest Hill that we've got several child-friendly venues for drinks and meals, so if you want to try and arrange some meet-ups you could for example post on the forum that you're planning to be in the Honor Oak, or the Dartmouth Arms, at a particular time on a particular day with baby in tow and would any other mums be interested in joining you?

A bit further afield but I can also recommend Friday afternoons in either the Mag or the Plough on Lordship Lane, East Dulwich. Both pubs run a 'baby club' on Friday afternoons where they clear a space and lay out some toys so that parents can meet there for a drink and there's a space for their babies and toddlers to play. I sometimes go with friends and have at other times just headed down there to see who's there and have a chat.