In a video clip posted at about 09:00 BST, he can be seen walking up behind the group in the middle of Mansell Street and snatching banners from them.

He also smacked a phone out of a protester's hands and shoved several other climate activists in the group of about a dozen people.

A spokesperson for the Met Police said it happened before officers arrived.

Just Stop Oil also held another traffic-blocking walk nearby, from Queen Victoria Street to Fleet Street, in the City of London.

It has been holding daily slow-march protests on roads since 24 April, sparking public anger at disruption to drivers. Similar traffic-blocking tactics have long been a source of frustration to motorists held up by activists.

The man smacked a phone out of a protester's hands

A spokesperson for the Metropolitan Police said: "The Met and City of London Police are aware of an incident in which a member of the public appears to have remonstrated with Just Stop Oil protesters this morning, 19 May, in the City of London, before the arrival of police.

"At this stage, we are not aware that any allegations have been made in regard to this matter. We completely understand the frustration and anger of London's communities when protesters walk slowly in the roads.

"We urge people not to intervene and to wait for the arrival of police, who will attend the scene promptly."

A spokesperson for Just Stop Oil said: "We understand how frustrating it can be to be disrupted, however, as of this morning, 13 people are dead and 13,000 people have had to be evacuated from their homes in Italy, due to six months' worth of rain falling in a day and a half.

"The disruption we are seeing on British streets is nothing compared to the disruption wrought if we do not stop licensing new oil, gas and coal."

Just Stop Oil is calling for an end to all new oil, gas and coal projects in the UK and says its protests will continue indefinitely.