@LondonCommuterSE I can vouch for the greatness that is CS Grupetto.
Brixton Cycles Club is also pretty damn good. Both clubs enjoy drinking and socials just as much as each other and we normally organize a hill climb every year CS Grupetto VS Brixton Cycles Club which is a right old laugh with bacon/quorn bacon sarnies at the top for supporter and riders ; )
You could also try but i dare say it, Dulwich. GULP.
Penge is a nice club too. Also De Ver in Streatham and Addiscombe. Depends where in SE you are too.