The rancour surrounding Catalonia’s disputed independence referendum has found an echo in London, where some members of a Facebook group called Españoles en Londres (Spaniards in London) proposed launching a “hunt for independence supporters” on Friday night, threatening to remove Catalan flags hung in windows, with the promise of a “night of broken glass” to follow.

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A posting on the group’s page credited to Jorge Arias Parra said: “A few friends and I are going to go to Camden tonight to hunt for independence supporters. We’ve noticed several windows where Catalan flags are hanging and we’re going to follow a route to take down secessionist flags ...”

The posting was followed by another where it was decided that anyone interested should meet at Camden Lock in north London at 11pm on Friday. “Those who want to join in should wear some sort of Spanish insignia. If there are any independence supporters who want to welcome us, they would be welcome too although I doubt they will as they tend to be cowards and manipulative snakes.”

Prompted by a reply from another member, Enrique García, who wrote “If we hit them I’m up for it”, Arias Parra went on to clarify the intentions of the group. “It’s going to be peaceful in principle, unless some screaming Catalan begs us to smash their face in.

“What we are going to organise for the next gathering is a night of broken glass if they don’t take down the Catalan flags. Today is just to get the maximum information possible about who they are, where they live and where they work.”

The threat provoked this response from a Facebook user identified as Maarc Gonzalez Motlló: “If you come by Hendon Central your head will be made independent of your body.”

Arias Parra went on to write that the intention was to create a database of Catalan independence supporters living in the area, with their addresses and workplaces. “If they don’t take the flags down,” he wrote, “we’re going to suggest to their landlords that they get house insurance and tell them of the risk to their houses if they exhibit Catalan fascist symbols.”

The Metropolitan police said that officers had been made aware of the threats, although there were no reports of any incidents.

The exchange provoked consternation among many users, with several expressing alarm and urging others to share the posting, while some wondered whether it was serious.

A Twitter thread started by a user identified as Arnau speculated whether the posting violated the UK’s hate crime laws, while other users asked if it contradicted Facebook’s own rules.

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Facebook’s community standards guidelines state: “We carefully review reports of threatening language to identify serious threats of harm to public and personal safety. We remove credible threats of physical harm to individuals.” The original posting by Arias Parra was removed, although it is not known if this action was taken by Facebook or by the Españoles en Londres group’s administrators.

The Office for National Statistics said that 43,000 Spanish citizens were living in London in 2014. The Spanish consulate said that there are 102,498 living in the United Kingdom.

A demonstration protesting against Spanish police violence in Catalonia was held at Piccadilly Circus in London on the day of the referendum.