Police officer hit G20 protestor - footage courtesy of YouTube
Metropolitan Police Commissioner Sir Paul Stephenson has asked Her Majesty's Chief Inspector of Constabulary (HMIC) to review policing tactics.
Denis O'Connor will conduct the review after two alleged assaults by police during the G20 protests in London.
Sir Paul said footage of the protests would be reviewed again.
The police watchdog will also probe the second alleged assault, in which a woman appeared to be struck by a police officer on 2 April.
Explaining the decision to launch a second independent investigation, Independent Police Complaints Commission Deputy Chair Deborah Glass, said: "It is appropriate to use our own investigators to deal with this latest incident arising from the policing operation relating to the G20 Summit.
"I have taken this decision bearing in mind the death of Ian Tomlinson and the volume of complaints made by the public about the actions and tactics of the police service during the policing of the G20 demonstrations."
She called for the woman seen in the footage, identified as 'Nicky', to come forward to the IPCC.
Sir Paul also stressed all uniformed officers must wear shoulder identification numbers so they can be easily identifiable by the public.
I want to be reassured that the use of this tactic remains appropriate and proportionate
Sir Paul Stephenson, Met Commissioner
Two officers have been suspended over two alleged assaults during the G20 protests.
Ian Tomlinson, a newspaper vendor, died after suffering a heart attack on 1 April minutes after coming in contact with a police officer who was seen shoving the 47-year-old to the ground in video footage.
On Tuesday new footage emerged of another officer who is seen hitting a woman in the face with his hand and on her leg with his baton after allegedly being sworn at.
Sir Paul said the G20 operation was one where officers had to ensure people had the right to protest.
Sir Paul said: "It is also the case that a number of complaints have been raised in relation to the tactic of containment and as to whether this achieves that balance.
"I want to be reassured that the use of this tactic remains appropriate and proportionate.
"Separately, I have already expressed my concern that the video footage of some police actions are clearly disturbing and should be thoroughly investigated.
"As well as the post-event investigation into those responsible for violence and disorder, I have also ensured that footage in police possession is reviewed to identify any other matters of individual police conduct that may warrant investigation."
He added that uniformed police officers should be identifiable at all times by their shoulder identification numbers.
"The public has a right to be able to identify any uniformed officer whilst performing their duty."
Home Secretary Jacqui Smith welcomed the call for review saying: "This is consistent with the police's commitment to continually review and examine their operations, so they can continue to meet the difficult challenge of balancing people's rights to peaceful protest while keeping the peace and maintaining public safety.
"We recently reformed HMIC to increase their capacity to provide this type of advice and it will be the Government's role to ensure that any lessons are disseminated nationwide."
She added there were "obvious areas of concern" around the G20 protests.
A spokeswoman for London Mayor Boris Johnson welcomed the referrals to the IPCC adding:"There are clearly concerns about some aspects of the policing of the G20 protests.
Kit Malthouse, deputy chairman of the Metropolitan Police Authority, said: "It is vital that the police retain the trust of Londoners and a thorough review by the HMIC will be crucial to help inform conclusions about how public order events should be policed in the future."
The MPA will question the commissioner on the alleged assaults and policing the G20 protests on 30 April.
After the new footage of the alleged assault emerged, opposition members of the London Assembly said the latest incident proved Mr Tomlinson's alleged assault was not an isolated incident.
Several London Assembly members also criticised some officers for "hiding" or "obscuring" their identification numbers.
It later emerged that the woman at the centre of the second alleged assault, is to be represented by PR agent Max Clifford.
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