Eleven people were arrested and three police officers were injured in British May Day protests today, Scotland Yard said.
Three police officers had been struck on the head by missiles but none of them required hospital treatment, police said.
Eleven people were arrested in the marches, police said. The biggest concern in London had been the afternoon's "May Day in Mayfair" mass action.
One website told how Mayfair is "one of the most opulent and cloistered areas in the capital, full of luxury pads, exclusive shops, fancy hotels and national embassies".
Teenagers were urged to "bunk off" school and join the event which the site says will happen "everywhere at once" to stay ahead of the police.
Among the speakers at a Trafalgar Square rally was former Labour MP, Mr Tony Benn (77), who told the crowd to loud cheers: "I remember as a kid listening to the voice of Hitler and we knew it would end in war because nobody stood up against fascism then.
"Now we find that all those hopes have been dashed as we return to imperialism, to war and to fascism."
The first protesters in London gathered at 7.30 a.m., joining two convoys of cyclists who then snaked their way through the capital disrupting rush-hour traffic.
They converged on Grosvenor Square where there was a substantial police presence around the US Embassy and the Canadian High Commission.
Another group set up a picket outside Horseferry Road Magistrates Court where seven members of the Wombles - White Overall Movement Building Liberations through Effective Struggle - are on trial.
Both events passed off peacefully although some motorists were clearly frustrated by the delays.
PA