Prime Minister Rishi Sunak condemned the incident as a “disgraceful act of vandalism”.

Leader of the Labour Party Sir Keir Starmer said the damage was “outrageous” and described Just Stop Oil as “pathetic”.

Members of the public were heard shouting “no” and seen running to intervene as the campaigners ran up to the stone circle at the Unesco world heritage site.

A spokeswoman for English Heritage described the spraying of the monument as “extremely upsetting” and confirmed the site remained open to the public.

She said the incident would not affect the annual summer solstice, with celebrations still planned to take place overnight on Thursday.

BBC correspondent, Paul Clifton, the first reporter to get to the scene shortly after the incident, said the three stones closest to the public path were “splattered” with the powder.

He added that many of the tourists visiting the monument were “slightly bemused”.

“Stonehenge managers and security guards are standing by the path,” he said.

“I’ve heard a suggestion that because it is powder paint and the weather is dry and sunny, it may perhaps be removed without lasting damage, but they will need experts to inspect the stone before forming an opinion.”

Just Stop Oil said the motivation behind the incident was to demand the next UK government end the extraction and burning of oil, gas and coal by 2030.

A spokesperson for the group said: “Continuing to burn coal, oil and gas will result in the death of millions.

“We have to come together to defend humanity or we risk everything.”

Mark Verbinnen, councillor for Amesbury East and Bulford, arrived at the site a few minutes after the incident.

He said many members of staff at the site were left “shaken”, particularly one who attempted to tackle a protester.

Mike Pitts, archaeologist and author of How to Build Stonehenge, said the impact of the action was “potentially quite concerning”.

He said: “The monument has been fenced off for decades and the megaliths’ surfaces are protected.

“They are sensitive and they are completely covered in prehistoric markings which remain to be fully studied and any surface damage to the stones is hugely concerning.

“A rich garden of life has grow on the megaliths, an exceptional lichen garden has grown. So it’s potentially quite concerning.”

A spokesman for Wiltshire Police said: “We responded to a report that orange paint had been sprayed on some of the stones by two suspects.

“Our enquiries are ongoing and we are working closely with English Heritage.”