Part of the Tower of London has been closed following reports of criminal damage to a display case containing the Imperial State Crown, part of the Crown Jewels.
Police said four protesters had been arrested following the incident just before 10am on Saturday.
They said it was reported that food had been thrown onto the case before two protesters left the scene.
Footage of the incident appears to show one demonstrator removing the large foil tray of apple crumble from a bag and slamming it against the glass.
Meanwhile, another pours a tub of bright yellow custard on the front of the case.
They then held up a sign which read "Democracy has crumbled - Tax the rich".
Police said in a statement: "Officers worked closely with City of London Police and security officers and four people have been arrested on suspicion of criminal damage. They have taken into custody.
"The Tower has been closed to the public while the police investigation continues."
The Metropolitan Police later said only the Jewel House at the Tower had been closed to the public while investigations continued.
A spokesperson for Historic Royal Palaces confirmed The Crown Jewels had not been damaged.
Take Back Power - which describes itself as a new non-violent civil resistance group - claims it was responsible.
The Imperial State Crown is built on a gold frame, with silver gem mounts housing 2868 diamonds, 269 pearls, 17 sapphires and 11 emeralds.
Fitted with a purple velvet cap and ermine band, some of the stones are famous in their own right, named the "Stuart Sapphire" and "Black Prince's Ruby".
It was originally made for King George VI in 1937, but is still used for major royal events, including the annual State Opening of Parliament.
It forms part of the Crown Jewels - a priceless collection which includes orbs, sceptres and crowns - and is considered to be the most famous of the nation's treasures.
(c) Sky News 2025: Crumble and custard thrown at State Crown display case in Tower of London
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