Critical Mass London: last friday of the month South Bank by National Theatre, 6.30pm

Fair enough. The point of critical mass is to reclaim the streets from motorists.

It's always worth pointing out that as an 'organised coincidence', Critical Mass isn't very easy to pin down, and part of its enduring appeal is that people can project all sorts of 'points' onto it. Endless debates are constantly had around the world what the 'point' is, but so far consensus has proved fairly elusive. :)