Boris Johnson’s convoy was involved in a minor collision outside Parliament when a protester ran towards the cars.
This forced the lead car in the convoy to brake suddenly causing the escorting vehicle to collide with the saloon car carrying Mr Johnson.
A visible dent was seen in the prime minister’s Jaguar as the convoy drove off towards Downing Street.
No 10 confirmed Mr Johnson was in the car and said there are no reports of any injuries.
The demonstrator, who was later detained by police, had been protesting about Turkey’s action against Kurdish rebels.