PlayThe police officer thought to be shown in video footage striking Ian Tomlinson, who died during the G20 protests, has come forward.
The Independent Police Complaints Commission (IPCC) is probing his death after video footage showed the newspaper vendor being struck by an officer during demonstrations outside the Bank of England last Wednesday.
ITN footage shows a riot officer seemingly striking out at Mr Tomlinson with a baton before pushing him to the ground.
A Guardian newspaper video had previously shown the 47-year-old being hit and pushed over by a partially-masked officer as he walks away from a police line with his hands in his pockets.
The images will be crucial to the IPCC investigation, which has already ordered that a second post-mortem examination is carried out on Mr Tomlinson who collapsed and died of a heart attack shortly after the footage was captured.
The Metropolitan Police officer will be interviewed by IPCC investigators "as soon as possible", a spokesman said.
A Scotland Yard spokesman said: "Earlier today a Metropolitan Police Service officer identified himself to his team leader as being potentially involved in the incident shown on the video footage.
"A total of four MPS officers, inclusive of this officer, have now come forward with potentially relevant information in relation to the investigation into the death of Mr Tomlinson."
And IPCC Commissioner and deputy chairman Deborah Glass said "We are pleased that we now have what appears to be valuable information relating to this incident. Several police officers, including the officer himself, have come forward. It is our intention to interview this officer as soon as possible."
Another witness has been reported saying Mr Tomlinson was manhandled about 15 minutes earlier as he tried to cross a police cordon on his way home from work.
Metropolitan Police Commissioner Sir Paul Stephenson said the images "raise obvious concerns" and should be investigated fully.
After watching the footage, Mr Tomlinson's son, Paul King, 26, said his father left work selling the Evening Standard at Monument Station at about 7pm. He was trying to make his way home but police at a number of barricades were not allowing people through.
He said the video showed police did have contact with his father but added: "Whether that was a cause to his death we are not to know.
"We want answers: why? Ian clearly had his arms in his pockets and back towards the police. There is no need for them to step in towards him. It clearly shows that Ian did have an altercation. Now we can say, yes he did. Up until now it has been 'if'. But now we've seen it, we want answers."
The footage was reportedly shot by a fund manager from New York who was in London on business. It was taken at about 7.20pm at Royal Exchange Passage.
The man, who has not been named, said: "The primary reason for me coming forward is that it was clear the family were not getting any answers."
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