This is the extraordinary moment a police car collided with a cyclist, drove over a bike and then sped off after tensions flared during a mass bike ride in central London.

The police 4x4 hit the cyclist – causing him to stumble backwards and drop his bike – and then crushed a second bike under its wheels before racing off on Friday night.

Witnesses described the incident at the junction of Vauxhall Bridge Road and Millbank as a “hit and run” as they slammed the officers’ actions.

Scotland Yard said police were trying to drive away in their BMW X5 after being “targeted by demonstrators”. They drove over the bike after it had been deliberately left in the road as an obstruction, a spokesman said.

The incident took place just after 9pm during the monthly Critical Mass bike ride, which sees hundreds of cyclists take to the streets for a group ride through London.

One observer who filmed the confrontation said it was “completely unacceptable”.

IT consultant John, 25, who did not want to give his last name, told the Standard: “I can imagine the police line is that they felt threatened, but frankly they’re armed police officers – do a bunch of cyclists pose a threat to them?

“Was it necessary to run over this kid’s bike? The police were trying to push people out of their way with the car.

“I think it’s entirely fair to call it a hit and run. The police were involved in an accident, they completely crushed a bike, and then they ran away.”

John said cyclists were remonstrating with the officers in the car after they had earlier “collared” a cyclist and treated him roughly.

Witnesses said they “wrestled” him off his moving bike and then dragged him across the road.

“They collared this one guy very forcefully,” said John.

“I started filming as the level of force the officers used was disproportionate.

“I don’t know why they collared this guy, but it looked like they wanted to make an example of them to the rest of the group.”

A spokesman for the Metropolitan Police said: “At approximately 9.10pm on April 29, police became aware of a demonstration involving a number of cyclists at Vauxhall Bridge.

“During this a police vehicle was targeted by demonstrators. As it tried to drive away, the vehicle ran over a cycle that was left in the road as an obstruction.

“No one was injured.”