What should you do if you discover an anarchist living next door? Dust off your old Sex Pistols albums and hang out a black and red flag to make them feel at home? Invite them round to debate the merits of Peter Kropotkin's anarchist communism versus the individualist anarchism of Emile Armand? No – the answer, according to an official counter-terrorism notice circulated in London last week, is that you must report them to police immediately.

This was the surprising injunction from the Metropolitan Police issued to businesses and members of the public in Westminster last week. There was no warning about other political groups, but next to an image of the anarchist emblem, the City of Westminster police's "counter terrorist focus desk" called for anti-anarchist whistleblowers stating: "Anarchism is a political philosophy which considers the state undesirable, unnecessary, and harmful, and instead promotes a stateless society, or anarchy. Any information relating to anarchists should be reported to your local police."

The move angered some anarchists who complained that being an anarchist should not imply criminal behaviour. They said they feel unfairly criminalised for holding a set of political beliefs.

The feeling of disproportion was compounded by the briefing note author making a similar request about Islamist terrorists a few lines further down. Under an image of flag with a gold dot beneath some Arabic script it added: "Often seen used by al-Qaida in Iraq. Any sightings of these images should be reported to your local police."

"It unfairly implies that anyone involved in anarchism should be known to the police and is involved in an dangerous activity," said Jason Sands, an anarchist from South London. "There is nothing inherently criminal about political philosophy whatever it is. The police work under the convention on human rights which disallows discrimination against people because of their political beliefs and even the request for information would seem to be in breach of that. It also seems to be a bit useless as a way of gathering intelligence. It isn't focused on anything specific and they are just asking for general information. Imagine calling up and saying 'there's an anarchist in my building. What should I do?' It doesn't make sense."

The note was issued from Belgravia Police Station as part of Project Griffin which aims to "advise and familiarise managers, security officers and employees of large public and private sector organisations across the capital on security, counter-terrorism and crime prevention issues".

Sean Smith, external relations officer for Solfed, the British section of the anarcho-syndicalist International Workers' Association, said of the call for whistleblowers: "It's pretty absurd, but not surprising, when the state seeks to criminalise ideas it deems to be dangerous to its own survival".

"We are a revolutionary union initiative," he explained. "Members of our organisation believe in bringing about radical social change through workplace and community organising, not acts of terrorism. We have made extensive information about our ideas and strategy freely available online."

Small groups of anarchists masked and dressed in black did cause some damage to shop windows in central London during anti-cuts demonstrations in the Spring, but there has been little activity of late. The next big anarchist event in London appears hardly likely to concern the police. It is a book fair in October with "all-day cabaret starring assorted ranters, poets, singers and comics; all-day film showings and two kids' spaces".