Or, slightly more affordable, cawl, singing, beer and dancing at the London Welsh Centre for £5
I'll be there from 8.30. In fact I am there every Thursday, I have joined the weekly lessons and usually stay on for the Cylch Siarad in the bar afterwards (open to all to practice Welsh).
There is also another guided walk (in English) on the 24th Feb (the last one was very interesting), and a Welsh Emporium on the 3rd. Further ahead, there's a gin tasting and a gig from the wonderful Calan.