A cyclist has launched a High Court challenge against police claims that a long-running monthly cycle ride through London is unlawful.
Critical Mass rides involve cyclists taking to the streets once a month to celebrate safe cycling.
Police say it is unlawful because the rides have an organiser and fail to give notice of a route.
Des Kay, of Kingston, south-west London, argues it is a procession. A decision is due in a few weeks.
His lawyers argued that the monthly rides are lawful because they fall within an exception for processions that are "commonly and customarily held".
They also said an organiser is not required and notice cannot be given to the police.
The monthly rides first took place in April 1994, and have since been held on the last Friday of every month.
However, last September police handed notices to cyclists saying that under the Public Order Act police needed to be notified of demonstrations.
At the time, police said it was not an attempt to prevent the rides from going ahead and they were committed to "facilitating lawful protests and demonstrations".
Des Kay said: "Cycling in London needs all the encouragement it can get.
"Critical Mass is an important celebration of cycling in the capital and makes a real contribution to safe cycling by giving cyclists the confidence they need."
Phil Michaels, of Friends of the Earth, whose justice centre will act for Mr Kay, said: "The police have tried to use public order legislation to undermine a perfectly lawful and safe cycling event."