Four people have been arrested after custard and apple crumble were flung at a display case containing part of the Crown Jewels at the Tower of London.
Police were called on Saturday after the case containing the Imperial State Crown was defaced.
The Metropolitan Police said four people had been arrested on suspicion of criminal damage, and the Tower's Jewel House has been closed to the public while the police investigation continues.
Take Back Power, which describes itself as a new non-violent civil-resistance group, claimed it was behind the act.
The group said it carried out the stunt to demand that the UK government establish a permanent citizens' assembly, a "House of the People,” with the power to "tax extreme wealth and fix Britain.”
Footage shared by the group on social media showed one protester removing a large foil tray of crumble from a bag before slamming it against the glass protecting the Imperial State Crown.
Another then poured a tub of bright yellow custard on the front of the case.
One protester shouted that democracy has crumbled, while another added that Britain is broken.
Surprised tourists could be seen reacting to the stunt, while a Tower of London staff member spoke into her radio.
