Boris Johnson’s car was involved in a minor collision with a security vehicle after a protester targeted the convoy outside parliament.
Video footage showed a man running in the road outside the Palace of Westminster as Mr Johnson left through the gates following prime minister’s questions on Wednesday.
The lead car was forced to stop to avoid the protester, who had been demonstrating about Turkish action against Kurdish rebels, prompting an escort vehicle to shunt into the back of Mr Johnson’s car.
The vehicles then drove off, with a dent clearly visible in the back of the prime minister’s Jaguar.
Downing Street confirmed the prime minister was inside the car at the time of the incident.
A No 10 spokesman said: “Yes, that was the PM’s car.
“I think the video speaks for itself as to what happened. No reports of anybody being injured.”
The protester was detained by police and taken into the Palace of Westminster by officers.
A Metropolitan Police spokesman confirmed that two police vehicles were involved in a collision in Parliament Square.
The spokesman said: “The police vehicles were part of a security movement.
“A pedestrian is reported to have stepped onto the road, causing the vehicles to suddenly stop, which has led to two of the vehicles in the convoy being involved in a damage-only collision.
“No injuries have been reported.
“A man, no further details at this time, was arrested at the scene for offences under Section 5 of the Public Order Act and for obstructing the highway.
“All vehicles were able to drive from the scene.”