Word (and some sighted paper leaflets) says Critical Mass started in London in April 1994

We celebrated its 30th anniversary in April 2024

We celebrated its 20th anniversary in April 2014

For earlier happenings and anniversaries you’d have to check out older sites …

http://www.criticalmasslondon.org.uk/

http://www.urban75.org/photos/critical/

http://criticalmass.wikia.com/wiki/London