A police car being driven by a female officer did not have its sirens on when it fatally struck a man in his 60s crossing a road, it was claimed.

Mechanic Arif Miah, 29, said the black man was already dead before the air ambulance landed.

Mr Miah of Morden, was working less than 200 yards from where the crash happened down the road in Western Road, Mitcham at 11.30am on Wednesday.

Speaking from the police cordon he said: "I was here the whole time and I definitely would have heard it if it was coming across with a siren.

"The only thing I heard was probably after it happened - three sirens going past. And I heard the helicopter.

"I would say no it didn't have it on - I don't think I heard a siren before those ones.

"They are always flying up and down here.

"I went out to see what was going on and asked a police officer. He was putting the cordon up.

"He just said to me that it was a female officer that hit the man. He actually told me that he died at that time. It was probably five minutes before the helicopter landed."

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The victim's body was seen being removed by a private ambulance at around 3.30pm a few yards from the marked police car, which had a large dent in its bonnet and smashed windscreen.

A 30-year-old security guard from Mitcham, who was at work in a Lidl store nearby, said: "There was no actual sirens blaring.

"I would have heard them if he went past with them on."

Scotland Yard refused to disclose what 999 call the officer was responding to, referring queries to the police watchdog.

An Independent Office for Police Conduct spokesman also refused to reveal what the call out was to, and said: "The IOPC has launched an independent investigation following a fatal collision in Mitcham, south London today (5 June).

"The Metropolitan Police Service alerted us of the crash, involving a pedestrian and a police car and investigators have deployed to the scene.

"Sadly the pedestrian, a man in his 60s, has since died.

"We declared an independent investigation at 12.50pm and have begun gathering evidence."