A trendy London cafe that sells only breakfast cereals at more than $8 a bowl was targeted during a protest about affordable housing.
Police were called to the Cereal Killer cafe, in Shoreditch, East London, when around 200 protesters wearing pig masks terrified customers, the UK Telegraph reported.
Paint was thrown at the cafe and the word "scum" was sprayed one of the windows.
The riot was promoted on social media, the Telegraph reported.
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The demonstration was allegedly organised by a group called Class War.
A Facebook statement said: "Our communities are being ripped apart - by Russian oligarchs, Saudi Sheiks, Israeli scumbag property developers, Texan oil-money twats and our own home-grown Eton toffs. Soon this City will be an unrecognisable, bland, yuppie infested wasteland with no room for normal (and not so normal) people like us."
The cafe owner said, "there were children there - they were terrified".
One arrest was made and one police officer suffered minor facial injuries in the disorder, a Metropolitan Police spokesman said, the Telegraph reported.
The cafe gained media attention when it opened last December after a interviewer asked if local people could afford to pay £3.20 (NZ$8.40) for a bowl of cereal.