Overlords are in Becontree, which is near Barking on the District line. They play
40k in a scout hall behind a church, have a pretty regular attendance, lots of tables, tons of scenery and pretty much monthly events/tournaments.
Their club 'night' is 3pm-7pm every Sunday.
http://www.theoverlords.co.uk/ If you're in south london, then I believe there's still a club called South London Warlords, who run from a church hall in Dulwich. As far as I remember, they're quite a sizeable club, and play a lot of historicals as well as
40k/Fantasy.
In fact, yes - they are huge. They seem to organise the Salute event each year at Excel - their website is
http://www.salute.co.uk/