London - A police officer in Britain at the centre of a row over the death of an innocent man during last week's G20 protests in London has come forward, Scotland Yard said Wednesday.

The development came amid a growing furore over amateur video footage published by the Guardian newspaper Wednesday which showed a police officer hitting the man before "shoving" him to the ground on the fringes of the protests on April 1.

Ian Tomlinson, a 47-year-old newspaper seller, died from a heart attack minutes later.

"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 Scotland Yard spokesman said.

A total of four officers had now come forward with "potentially relevant information" regarding the investigation into the incident.

London Mayor Boris Johnson has described the footage as "very disturbing" and several members of parliament (MPs) have urged a criminal investigation.

In an unusual move, Scotland Yard chief Paul Stephenson conceded that Tomlinson's death raised "obvious concerns" that needed to be fully investigated.

"My thoughts are with Mr Tomlinson's family at this time. The images that have now been released raise obvious concerns and it is absolutely right and proper that there is a full investigation into this matter," said Stephenson.

Home Secretary Jacqui Smith said it was "extremely important" that the probe into the "sad death" of Tomlinson should be completed "as quickly as possible."

She did not rule out that the current investigation by the police watchdog, the Independent Police Complaints Commission (IPCC), would be followed by a criminal investigation.

Late Wednesday, the IPCC ordered a second post-mortem examination in an effort to determine if there were any external factors behind the heart attack.

Video footage published Wednesday on the website of the Guardian newspaper showed Tomlinson walking with his back to a group of police officers, hands in his pockets, when a helmeted officer in riot gear lunges at him from behind.

Tomlinson, who was not protesting, is seen falling heavily to the ground and complaining to the officers before being helped to his feet by passers-by on April 1, the eve of the summit of Group of 20 (G20) nations.

Tomlinson walked on, but collapsed with a heart attack shortly afterwards near the Bank of England, where the demonstrations had taken place and protestors were still milling around.

Initial police reports made no mention of any police contact with the victim who, according to his family, was not involved in the protests.

David Howarth, the justice spokesman of the opposition Liberal Democratic Party, said the footage showed a "sickening and unprovoked attack" by police that required a full criminal investigation.

His call was backed Wednesday by Labour MP David Winnick, who urged Smith to make a "full statement" to parliament after the current Easter recess.

Winnick, a member of the Home Affairs Select Committee, said questions would be asked about "misleading" police statements in the hours after Tomlinson's death.

He compared the case to the killing by police of innocent Brazilian Jean Charles de Menezes by anti-terrorism officers in London in July, 2005.

"In view of the unfortunate death of Jean Charles de Menezes four years ago, there is all the more reason for concern, which I share, that all the circumstances of this case must be thoroughly looked into," Winnick urged.

The new photographs showed that Tomlinson had been "hit by a police officer," said Winnick. There would, therefore, be "anxiety about the thoroughness of the inquiry."

The family of the dead man also asked for "answers" and called for witnesses to come forward.

The video footage had confirmed that there had been "contact" between his father and the police, said Tomlinson's step son, Paul King.

"Now we've seen it, we want answers," he said. (dpa)