Police arrested 50 people last night during the Million Mask March after the Anonymous protest turned violent.
Three police officers were hospitalised with injuries not thought to be life-threatening, and a police horse was injured near Buckingham Palace, throwing its rider. The rider was taken to hospital as a precaution and the horse returned to stables for treatment. A police car was set on fire, although the London Fire Brigade extinguished the blaze "within minutes".
Earlier in the day, police had discovered knives, smoke and paint grenades, gas canisters and lock picks after conducting a stop and search on three men. The individuals, aged 38, 50 and 55, were arrested on suspicion of being in possession of offensive weapons and taken to a central London police station, where they remain in custody.
But the majority of arrests were made at Trafalgar Square and Parliament Street, Whitehall when the protest continued after 9pm, one of the Public Order Act conditions that the march was allowed under.
Commander BJ Harrington said: "We facilitate hundreds of protests every year in London peacefully and with the co-operation of the organisers. On this occasion a group of protestors chose not to engage with police or adhere to the conditions of the protest and were intent on criminality.
"I'd like to thank those who conducted themselves in a peaceful manner and as well as Londoners for their patience and tolerance whilst anti-social and intimidating behaviour was happening."
He added: "Officers have been hospitalised, a police horse suffered injuries and a police car was criminally damaged during the course of the protest which is completely unacceptable.
"I praise the professionalism and restraint that officers have shown in the face of hostile provocation and enabled the policing operation to pass without major incidents. We will bring those responsible for the criminality to face justice."