Three police officers were injured and 40 people were arrested after disorder broke out at a protest near Downing Street on Tuesday night.
One officer suffered a serious facial injury after she was hit by a bottle thrown from the crowd, while two officers had minor injuries after being “assaulted”, the Met Police has said.
The suspect who threw the bottle has not been identified but officers are investigating, the force added.
Police have estimated that between 8,000 and 10,000 people attended the protest on Whitehall in Westminster, which was organised by a coalition of groups including the Palestinian Solidarity Campaign.
The protest began at 6pm and police imposed conditions under the Public Order Act requiring the action to end at 8pm.
Police have said the “vast majority of those in attendance” left at the required time, but around 500 people remained and continued to protest.
The Met said in a statement: “Officers engaged extensively before making a number of arrests for failing to comply with conditions. As they moved in, some in the crowd resisted physically, requiring officers to use force to extract those who had been arrested.”
The force said some protesters then set off on a breakaway march down nearby Bridge Street, outside Westminster Tube station, where officers put up cordons to detain the group.
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Police said officers went into the crowd shortly before 10pm to arrest those suspected of leading the breakaway protest, with 40 people held for offences including breaking the Public Order Act, obstruction of a highway and assaults of emergency workers.
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The force said the three officers who suffered injuries during the protest had been dealing with the breakaway march.
Police said all protestors had left the area and Bridge Street reopened at around 2am on Wednesday.