Part of the Tower of London has been closed to visitors after food was thrown at a display case containing the crown jewels in a protest against inequality in the UK.

Four people were arrested on Saturday after the action, which was claimed by Take Back Power – a self-described non-violent civil-resistance group. It said custard and apple crumble was flung at the case, which contained the imperial state crown.

Scotland Yard said: “Four protesters have been arrested following criminal damage at the Tower of London. Police were called at 09.48hrs on Saturday 6 December to the Tower of London following reports of criminal damage to a display case, containing the state crown.

“It was reported that four protesters threw suspected food on to the case before two left the scene. Officers worked closely with City of London police and security officers and four people have been arrested on suspicion of criminal damage. They have been taken into custody.”

The Tower of London, one of the capital’s most popular tourist attractions, was partially closed to the public while the police investigation continued.

Take Back Power said it carried out the stunt to demand the UK government establishes a permanent citizens’ assembly – a “House of the People” – with the power to “tax extreme wealth and fix Britain”.

Footage shared by the group showed one demonstrator removing the large foil tray of crumble from a bag and slamming it against the glass protecting the crown. Another repeatedly poured a tub of bright yellow custard on the front of the case.

The demonstrators then opened their coats to show their T-shirt slogans reading “Take Back Power”, before one shouted “democracy has crumbled” and another shouted: “Britain is broken. We’ve come here to the jewels of the nation to take back power.”

The group released a statement, in which it named one of the activists as 19-year-old Zahra Ali, a student from London. She said: “Our country is crumbling before our eyes. We have homeless people dying on the very streets that King Charles passed on his way to the coronation, whilst there are more empty homes than unhoused people in this country. It’s time the ultra-rich pay their fair share.”

Surprised tourists could be seen reacting to the stunt, while a Tower of London worker approached, saying: “Excuse me, excuse me”, as she radioed for help.

Initial reports suggested the whole of the site had been shut. The Metropolitan police later said only the Jewel House had been closed.