Addison Lee drivers told to defy bus lane law (and to just say SMIDSY)

All true yet as a protest which was widely publicised it would be less annoying for drivers than waiting for 20 minutes while the critical mass goes past. There would need for a huge build up and publicity about 'middle of the lane day' . We may have enough 'critical mass' of riders especially during the commute for it to succeed. And it could only work in London at the moment

I think it's a mistake to mix up good, everyday, cycling practice with protests. It's hard enough to win the argument about us having the right to take up assertive positions at the best of times; having those positions portrayed as a one-off demonstration won't help at all.
And that is leaving aside whether or not a protest would have any effect - I don't think it would. Critical Mass gets mentioned but this, and everything else that has happened in the last few years, just goes to prove again what an ineffective campaigning tool it is.