The annual Million Mask March, organised by hacktivist collective Anonymous, took place yesterday (Guy Fawkes' Day) in cities across the world.
In Washington DC, protesters attempted to enter the headquarters of biotechnology giant Monsanto, which has suffered a backlash in recent years for producing carcinogenic pesticides and genetically-modified products.
It was in London, however, where the protests became most violent. At least 50 people were arrested, mostly for public order offences.
The march was due to end at 9pm and the majority of arrests were made after breaches of police 'kettling' in St Martin’s Place, Trafalgar Square and Whitehall.
Three police officers were injured and treated in hospital and two people were arrested for assaulting a police officer.
Scotland Yard say that six police horses were injured, and some protesters were treated for injuries at the scene.
Three men, aged 38, 50 and 55, were arrested on suspicion of having weapons.
Meanwhile an unattended police car was set alight and damaged, in a side alley away from the main body of the protest.