There's a singaround this Sunday, 13 March at The Crystal Palace Tavern
(corner of Crystal Palace Road and Underhill Road, East Dulwich, SE22)
http://www.thegooseisout.com/aboutus.html#evec
Went to the last one and it was very well attended, fun, friendly and a great pub. Can't make it this Sunday unfortunately but i's every second Sunday of the month.