The Metropolitan Police have won a court battle giving them control over London's Critical Mass cycle ride.
The ride celebrates safe cycling
Two Appeal Court judges overturned a High Court ruling that the event was lawful and organisers must now notify police giving a date, time and route.
Every month cyclists gather on the South Bank and ride through the city in the evening to celebrate safe cycling.
Now police will have the power to make arrests under the Public Order Act if they are not warned about the route.
The legal battle began in September 2005 when, before the start of that month's ride, police handed out a letter to participants stating the Critical Mass rides were not lawful.
Police said "organisers of public processions" were required by law to give at least six days' notice of the date, time and proposed route, as well as their names and addresses.
This resulted in one of the regular Critical Mass riders asking Lord Justice Sedley and Mr Justice Gray to rule in the High Court that the police were misinterpreting the law.
The court heard the rides had no organiser and no fixed route and ruled that, as "customarily" held events, prior notice was not required under the Act.
At Monday's appeal hearing, Lord Justice Wall, the judge who found in favour of the cyclists, said to rule that Critical Mass fell under the auspices of the Public Order Act was "potentially oppressive".
"The police, in my judgment, know what the cyclists are going to do. They are going to ride around the Greater London area," he said.
"That is a perfectly lawful activity, and if, for any reason, it ceases to be so, the police have ample powers to intervene."
London mayor Ken Livingstone's road safety ambassador Jenny Jones had earlier urged the police to allow the rallies to go ahead as planned, the judge said.
However, Lord Justice Leveson said cyclists came together at a fixed point, but the lead riders chose the course and where the rally finished.
"A procession cannot, in my judgment, become common or customary if no route or end point is ever the same," he said.
Sir Mark Potter, the President of the High Court Family Division, also found for the police.
Jenny Jones, a Green Party member of the London Assembly, said in a statement: "This decision is bad news for everyone, as it will end up with the police wasting time arresting innocent cyclists like me, rather than arresting real criminals.
"Critical Mass is a lively, but peaceful get-together of cyclists which has been going on for over a decade without any major incidents.
"Arresting cyclists at Critical Mass will be like arresting a group of passengers for gathering at Westminster tube station during the rush hour."
The London ride is part of a worldwide phenomenon and has taken place on the last Friday of the month, every month, for the past 13 years.