A Downing Street spokesman said: “Mr Johnson was travelling in the car at the time.
“I think the video speaks for itself as to what happened.
“No reports of anybody being injured.”
Number 10 has characterised the event as a “small accident”.
After the cars drive away, police begin to try and clear protesters from the road.
A police van can be seen arriving with more officers to assist.
The Prime Minister was leaving the Westminster estate following Prime Minister’s Questions.
Mr Johnson clashed with Labour leader Sir Keir Starmer over a number of issues.
The two senior figures went back-and-forth over child poverty, school reopenings and local councils.