According to Indymedia.org.uk, Superintendent Gomm of the Metropolitan Police's CO11 Public Order Branch wrote an open letter to Critical Mass riders, telling them future events would be unlawful.
"Organisers of public processions are required by law to notify police at least 6 days before the event occurs of the date, time, proposed route and the name and address of an organiser. Failure to do so makes the event unlawful
"Demonstrations within a designated area around Parliament must also be notified, and anyone taking part in an unauthorised demonstration commits an offence.
"These cycle protests are not lawful because no organiser has provided police the with the necessary notification.
"It is preferable for all parties if a lawful event can be safely facilitated, rather than the Police having to enforce legislation."
In the US, where Critical Mass began in the 1980s, the New York ride has come under fire from authorities.
In 2004, New York tried to get a federal judge to ban Critical Mass cyclists from riding in a large group without a permit. And last year 'the Mass' hit the headlines when 250 cycling protesters were arrested after picketing the Republican National Convention took place in New York City.
According to Salon.com thousands of cyclists were guilty of "surging up Sixth Avenue, then across town and down to the East Village, they'd taken over the streets, blocking traffic, infuriating commuters and taxi drivers and reveling in their own numbers."
The New York Times has been sniffy, too: "Part of the conceit of Critical Mass is that it is not organized or led by anyone in particular; it simply happens."