A celebrated independent cinema was forced to cancel a screening of a controversial film on Brighton and Hove Council's orders.
Duke of York's in Preston Circus, Brighton, pulled the anti-war documentary at the last minute after an environmental health officer raised concerns over its lack of a certificate.
Cinema staff say they were told police had contacted the council to inform them of the potential breach of their licence.
They say it is the first time in recent memory a film has been pulled for that reason.
The film-makers are accusing police of deliberately interfering with their freedom of speech.
But senior officers in Sussex Police's Brighton and Hove Division say the force played no part in a council officer's decision to contact the Duke of York's.
Films must have a certificate from either the British Board of Film Classification or councillors responsible for licensing before they can be shown commercially.
The cinema apologised for the cancellation and said it should not have scheduled the film without checking its certification.
Felicity Fenton, assistant manager at the cinema, said: "We were only contacted late this afternoon "The police contacted the council and the council contacted us.
"I've been here for five years. It has never happened before."
She acknowledged the cinema should have checked the film, which has been advertised since the end of February.
She said: "They are right. If we show the public an uncertificated film we are in breach of our licence.
"In the future we will be very careful about it."
The cinema hopes to reschedule the film for a later date.
Chief Inspector Laurence Taylor said police played no part in the controversial cancellation.
He said: "We would never get involved with certification of a film - it is not something we do.
"It was as much a surprise to us as anybody else."
After the cancellation the film was given two impromptu screenings at The Branch pub in London Road.
The campaigners hope to organise another screening today.
They believe the film's criticism of the police prompted the council's decision to enforce the licensing regulations.
The film is the story of Smash EDO's five-year campaign against the manufacture of weapons components at EDO MBM Technologies Ltd factories in Moulsecoomb and Fishersgate.
The activists believe the components are used in military actions in the Middle East which they claim are in breach of international law.
Several protesters have been arrested after locking themselves to factory gates, climbing onto their roofs and for 'bad karaoke' sessions where activists sing badly to disturb workers.
The group proudly boasts of its record of more than 40 arrests and its effect in bringing down the company's profits.
The film's advertising reads: "Using activist, police and CCTV footage plus interviews with those involved in the campaign, 'On The Verge' tells the story of one of the most persistent and imaginative campaigns to emerge out of the UK's anti-war movement and direct action scene."
Andrew Beckett, spokesman for the campaign said: "When the police are reduced to banning film showings via the back door another blow has been struck against our rights to free speech and free assembly."
Councillor Dee Simson, chairwoman of Brighton and Hove Council's licensing committee, said: "If there are ever any concerns about the ratings of films that are shown councillors are asked for advice.
"I haven't given any advice on that particular one.
"I know they would be in breach by showing anything that doesn't have a rating."