The law on public processions is governed by section 11 of the Public Order Act 1986. It requires organisers to notify the police in writing of their intention to hold a public procession, and to provide details of the date, route and their own names and addresses.

The hundreds of cyclists who take part in Critical Mass say that, although the event is a regular occurrence, no one organises it and the route is never the same. And crucially it claims that it comes within an exception to the notice provisions because its event is "commonly or customarily held".

That exemption exists because the details of something that is commonly held will already be known to the police, and so notice is not required.

It's now up to the the country's most senior judges, the Law Lords, to decide if a public procession that is apparently not organised and follows a random route, is one that can be defined as "commonly or customarily held".

Full story:

http://news.bbc.co.uk/1/hi/magazine/7667183.stm

Me dogs are barking.

BHB,  contact the London Cycling Campaign (got a website) because they publish details of London's CMs in their bi-monthly magazine.  So they must know the organiser.

They may not want to pass on her details to you so ask to have yours passed on.

I went to a couple that originated near to Waterloo then later migrated to one closer to my home, near to Shepherds Bush but did consider them to be slightly tedious.  There's always plenty of quality right-on fanny too. 

Maybe Plymouth or Exeter have local cycling/environmental traffic groups you could contact.