OMG, there's been a murder at the Ilkley book festival!

The Grove Bookstore had decorated its window with copies of The Mitford Murders and The Seven Deaths of Evelyn Hardcastle.

Up the road, at the Cow and Calf rocks, someone had been bumped off. But the killers had got the wrong man.

Art had mixed with reality as a film crew came to town. The window display was real but the murder on the moors had been a scriptwriter’s invention.

Yet the story of a militant atheist crossing swords with an angry vicar at the town’s annual literature festival has been drawn from the pages of life.

Only last October, the evolutionist Richard Dawkins had addressed a sold-out audience at the King’s Hall. And at the inaugural event in 1973, the poet WH Auden had got into a fracas with a local vicar over which version of the bible to use.

“But we’ve never had an actual homicide,” said Alex Corwin, the festival’s head of marketing.

The organisation has licenced its name to the producers of Ilkley, a comedy movie about an inept murder plot, set against the backdrop of the festival.

It stars the venerable actor Sir Derek Jacobi as a high-churchman called Enoch, who puts out a contract on the fictional heretic booked for the event.

Yesterday, he was to be seen, in dog collar, scarf and cardigan, mixing with bemused locals as the crew got a chase scene down Railway Road in the can.

“I play a rabid Protestant,” he said. “He’s not a nice character – not very nice at all. But they’re often the most fun to play,”

The actor, whose other dislikable subjects include Adolf Hitler in the 1982 production, Inside the Third Reich, and whose credits range from I, Claudius to Gladiator and Gosford Park, said he had been attracted to the new project by its “very good, very multi-layered script”.

Yesterday’s shots – Sir Derek’s last in the film – see him arriving in Ilkley after discovering that the evangelical brothers he had despatched to see off the nonbeliever have got the wrong target.

The film’s producer, Helen Simmons, said the decision to use a real town as the setting for the fictitious story had been taken after the writer and director, Harry Michell, had visited Ilkley.

“We wanted that mixture of cultural hub and countryside, and the feeling that it was far away from everywehre else,” said Ms Simmons.

“And they attract such wonderful speakers at the real literature festival here.”

The filmmakers had spent a year in discussion with the festival organisers over the use of the name.

“They couldn’t believe it when we told them we had actually booked Richard Dawkins last year,” said Ms Corwin. “But he got out of town alive.”

Filming has been going on around Ilkley and Harrogate for the last few weeks, with Allerton Castle, near Knaresborough, doubling for the King’s Hall, and the regional investment agency Screen Yorkshire putting up some of the money.

Its head of investments, Hugo Heppell, said: ‘The combination of a highly entertaining script and of course, the location, which is so central to the story, made it an irresistible project for Screen Yorkshire.”

The film will be released in cinemas next year.