When I was a kid, the only thing I remember about St George's Day was that the Brownies and Cubs wore their uniform to school, later it became associated with unpleasant far right organisations but, mercifully, these days it seems to be an excuse for a big ol' party.
On the actual day, 23rd April, Borough Market is relocating to Trafalgar square for the day and there will be lots of food inspired street theatre http://www.londonisfree.com/2008/04/st_georges_day_at_trafalgar_squ...