New footage reveals Climate Camp incident - Video courtesy of The Sunday Times
The head of the police complaints watchdog is to give evidence in the Commons over the policing of the G20 protests in London.
Nick Hardwick, head of the Independent Police Complaints Commission (IPCC) will attend the Commons Home Affairs Select Committee on Tuesday.
Three cases, including the death of a man, have been referred to the body.
Mr Hardwick has questioned in the Observer why some officers apparently removed identity numbers from uniforms.
He also said police were "servants" not "masters".
In relation to his concerns over some officers suspected of removing their identification numbers, Mr Hardwick said: "I think that raises serious concerns about the frontline supervision.
They [the police] have to respond to the fact that they are going to be watched, there is going to be this evidence of what they have done
Nick Hardwick, IPCC chief
"Why was that happening, why did the supervisor not stop them?
"What does that say about what your state of mind is? You were expecting trouble?"
He also said the number of people who had filmed the protests on their mobile phones was proving a key factor in helping the IPCC determine whether complaints made against the police had any legitimacy.
The latest footage, released by Camp for Climate Action protesters at the London G20 demonstrations, shows a police officer striking a man, identified as IT worker Alex Cinnane.
Mr Cinnane, 24, is barged with a shield on the side of his head in the film, shown on the Sunday Times website.
The video, which was edited before it was released, does not show Mr Cinnane making any threatening behaviour towards the police officer.
Mr Hardwick told the Observer: "What's been important with all these pictures is we have got such a wide picture of what happened.
"I think that is challenging the police. They have to respond to the fact that they are going to be watched, there is going to be this evidence of what they have done."
He also said that typical complainants of police behaviour were from middle-class backgrounds, who did not previously have a jaundiced view of the police.
"If you are Mr and Mrs Suburban who have a good view of the police and think they do a good job, and they stop you and swear at you, then you are shocked and you complain."
The Camp for Climate Action claimed thousands of peaceful protesters were attacked without warning.
Frances Wright, a lawyer acting for the group, said: "What has happened has demonstrated the importance of protesters watching the police at least as much as the police watch them during protests."
She added that officers should be legally required to wear large, football-player-style numbers on the front and back of their uniforms, to cut the risk of officers concealing their identity.
The police tactic of "kettling", or containing demonstrators, is expected to be among the subjects discussed at Mr Hardwick's appearance at the Commons.
Ian Tomlinson died after he was pushed over by an officer
Her Majesty's Chief Inspector of Constabulary, Denis O'Connor, is also scheduled to appear.
Newspaper seller Ian Tomlinson died after being pushed over by police on 1 April and film footage also showed an officer hitting Nicola Fisher, 35, from Brighton, across the face with his hand and on her leg with a baton on 2 April.
BBC Home Affairs correspondent, June Kelly, warned that fresh controversial images could still emerge.
She said: "This is the third case the Met has now referred to the IPCC. With so many cameras out there more footage could emerge in the coming days."
Former Metropolitan Police Commander John O'Connor, warned the Commissioner, Sir Paul Stephenson, he was in danger of losing the support of rank and file officers if he turned the case into a "witch hunt".
Sir Ken Jones, president of the Association of Chief Police Officers (Acpo) said the "vast and overwhelming majority" of police taking part in the operation deserved the public's support.
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