Clashes at G20 protest Climate Camp - Video courtesy of The Sunday Times
The head of the police complaints watchdog has urged a debate on crowd control as he prepares to give evidence to MPs following the G20 police row.
Nick Hardwick has questioned in the Observer why some officers apparently removed identity numbers from uniforms.
The head of the Independent Police Complaints Commission also said police were "servants" not "masters".
He will attend the Commons Home Affairs Select Committee on Tuesday after the referral of three G20-related cases.
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 boss
"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 Climate Camp 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 footage, 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."
An IPCC spokesman confirmed Mr Hardwick would attend the Commons Home Affairs Select Committee on Tuesday to answer MPs' questions.
The police tactic of "kettling", or containing demonstrators, is expected to be among the subjects discussed.
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."
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