Two supporters of the campaign group Just Stop Oil were captured on camera smearing chocolate cake over the lifelike model of the British monarch on Monday.
In a video clip shared on the group’s Twitter page, the pair are seen removing their black clothing to reveal white “Just Stop Oil” T-shirts once they reach the podium housing waxworks of the royal family.
After throwing the cake, they tell the bystanders it is “time for action”.
“We responded quickly to an incident at Madame Tussauds after two people threw food at a statue at approximately 10:50hrs,” London’s Metropolitan Police said in a tweet on Monday.
Police later said four people had been arrested for criminal damage related to the incident.
Just Stop Oil said the pair were “demanding that the government halts all new oil and gas licenses and consents”.
Monday’s incident is the latest in a string of actions by activist groups across Europe designed to draw attention to the role of fossil fuels in climate change.
The painting, which is glazed, was undamaged.
The protests, however, have divided opinion.
Keir Starmer, leader of Britain’s opposition Labour Party, condemned the actions of the “arrogant” Just Stop Oil activists, saying their methods undermined their cause.
“I think they’re wrong, I think their action is wrong,” he told a caller on LBC Radio on Monday morning.
“I particularly think about the images we’ve seen of ambulances coming down the road, and not being able to get through because people have glued themselves to the road,” he continued.
“I think it’s arrogant of those gluing themselves to the road to think they’re the only people that have got the answer to this. They haven’t got the answer.”
“We cannot endorse these extreme and dangerous tactics which put our members at risk whilst they try to work,” the unions said.
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Sports broadcaster and former England football star Gary Lineker, on the other hand, was more sympathetic.
“Worth a listen, because, like it or not, no one will listen without disruptive protest,” Lineker told his 8.6 million Twitter followers, sharing an interview by journalist Owen Jones conducted with the National Gallery protesters.