The man was being pursued by the officer on a motorbike after failing to stop around 7.38am on Friday morning in Camden, northwest London.

The car crashed in Mornington Crescent, at the junction with Harrington Square, before the driver got out of the vehicle and was challenged by the officer, who drew his Taser.

Video footage posted on Twitter appears to show a scuffle before the man gets up and points a black firearm at the officer, who is attached to the Parliamentary and Diplomatic Protection Command, part of the specialist operations directorate within the Metropolitan Police.

He was arrested on suspicion of possessing a firearm and was taken to hospital before being detained, Scotland Yard said.

The weapon has been seized and will be examined to establish whether it is a genuine firearm or a replica.

No injuries were reported during the incident.

The unnamed officer's actions were hailed as "nothing short of incredible" by Chief Superintendent Roy Smith, who added: "He had no idea if the item being pointed at him was a replica or a lethal weapon and yet he maintained his composure and detained the suspect.

"Each day police officers put on the uniform and put themselves in danger to protect Londoners.

"This is a perfect example of the bravery and selflessness that they exhibit so often."

The force said it is aware of the video circulating online and has assured the public the officer's welfare was being taken care of.