By Dominic Casciani
BBC News Online
Stand-off: Confrontation at High Holborn
While May Day morning had appeared quiet, the afternoon was to be the real test.
As trade unionists began to gather in Trafalgar Square for the main TUC workers' rally, security cordons were being thrown up at buildings thought to be targets.
Among the protesters gathering in the square was 17-year-old Ben, a Dulwich College A-level student who had taken the day off "for a noble cause".
He was wearing a motorcycle helmet, face mask, surgical gloves and bubble wrap underneath his school blazer.
"It's not to make redecorating McDonalds any easier," he said with a smile.
Ben said he was against the war, capitalism, injustice and damage to the environment.
But one of the things he was most bothered about was damage to his own head.
Ben: Bunking off
"The coppers hit me last time. This time I've come protected," he said.
Half-a-mile away, 40 police officers were outside the headquarters of Shell Oil on The Strand.
Another target, the London offices of Lockheed Martin, a major US defence corporation, were boarded up.
As expected, protesters began gathering there just before 2pm.
It quickly turned into clashes. A few hundreds protesters had gathered outside the company's unmarked headquarters.
As a small group led by black-clad anarchists, tried to block High Holborn, one of the busiest junctions in central London, officers moved in.
A stand-off began which developed into a short running battle as a number of masked young men pushed at the officers.
The most damage appeared to be done to the police officer's pride as it appeared to take them by surprise. Compared to previous anti-capitalist protests, this was tame stuff.
Pro-capitalism: John Robertson
When police wearing body armour regained control, they imposed a special order on the crowd, effectively telling them they were going to be kept penned in until they agreed to follow a police-controlled route to Trafalgar Square.
Eventually, the anarchists agreed to do as they were told and started slowly, but reluctantly, moving towards the square.
Perhaps the most unlikely protester of the day so far was Canadian John Robertson.
He declared to the anarchists he was proud to work for capitalism and had to be extracted by police for his own safety as things got a bit heated.
Speaking afterwards, he asked why he could not also have his May Day protest.
"I love it here in London where you guys can have your May Day protests and say what you think," he said, waving his pro-capitalism banner.
Boarded up: Shops on Old Bond St
"I don't think that the anti-globalisation movement or anarchy has anything to offer. Capitalism seems to work pretty well to me so someone should stand up and say that," said Mr Robertson.
Earlier the protest group Critical Mass staged a bike ride to highlight the need for sustainable transport.
The protest group is well known throughout London for its ability to stop the traffic through the sheer will of hundreds of cyclists moving slowly.
This time, only a few turned up at the official start. There were so many journalists waiting for them at one stage it appeared there was a camera for each bike-riding protester.
Meanwhile, in the heart of London's West End, dozens more journalists were waiting for what had been billed as the first potential trouble spot of the day.
Shops along Old Bond Street, one of the most exclusive shopping areas, were boarded up as they waited for anti-fur protesters to picket designer shop Dolce and Gabbana.
Churchill: Parliament Square protection
In the end and almost an hour late, a dozen anti-vivisectionists turned up, effectively outnumbered by the police.
They unfurled a banner in front of the shop which was covered with corrugated iron sheeting to protect windows which reportedly cost £7,000 each.
There was no trouble, only a small demonstration against the use of fur from London Animal Action (LAA).
Among the group were protesters giving out leaflets in the name of Shac, one of the animal rights groups watched by the security services because of its actions against Huntingdon Life Sciences.