While not yet on a par with Rio or New Orleans, the Shrove Tuesday pancake races in Shoreditch are a fun local event, and worth experiencing if you are in the neighbourhood on the day.
As far as I know, the Shoreditch Shrove Tuesday pancake races are as close as London gets to the much-hyped extravaganzas of Rio or New Orleans. In addition – unlike their over-the-top cousins – you can enjoy a ringside view of the whole event and it is all over in less than half an hour. And you are unlikely to get sun stroke or a hangover.
The Shoreditch Shrove Tuesday pancake races are contested by teams of four people (preferably in fancy dress) who run up and down a back yard of the old Truman Brewery while flipping pancakes. This year, I managed to get there in time to see the bridal party (bride, groom, and a pair of bishops) make the most of the damp conditions and claim the frying-pan first prize. A couple of hundred spectators were there, and the "local" atmosphere (with plenty of raucous support) added to the fun.
After the races, the pancake van did a roaring trade. My cheese and spinach crepe (GBP4) did the business for me. There are plenty of other restaurants nearby (notably on Brick Lane, famous for its Bengali restaurants) if you are looking for something more substantial.
Unfortunately the Truman Brewery ceased production in the 1980s. However, much of the original architecture (including the beautiful big chimney and several Black Eagle motifs) is still intact and looking good.