The two dog-walkers look up at the hillside church of Saints Mary and Patrick in the Co Galway town of Avoca. The forecourt has been transformed into a muddy swamp. Blank-faced zombies moan menacingly, towers of flame shoot hundreds of feet into the sky. A vicar in drag tries to marshal order, while a man in a black, bejewelled cloak and pantaloons sits in a chair having make-up applied.

Pretty extreme, eh, I say to the dog-walkers.

“Nah. We had Matthew McConaughey here for Reign of Fire,” says one dismissively.

“And Ballykissangel for five years before that,” says the other. They walk off, distinctly underwhelmed.

The League of Gentlemen are in town to film the climax to The League of Gentlemen’s Apocalypse, a spin-off film from the highly successful TV series set in a village of the damned, populated by terrifying grotesques and misfits. When it made its debut on BBC Two in 1999, there was nothing like it — twisted sitcoms began and ended with Absolutely Fabulous — and it ushered in a new era of gleefully warped primetime comedy (Little Britain , Nighty Night).

The plot of the movie, as fans would hope, is complicated, perverse and rather silly: the four real-life members of the League of Gentlemen, Mark Gatiss, Reece Shearsmith, Steve Pemberton and Jeremy Dyson (except that he is played by the actor Michael Sheen, to confuse things further), come face to face with their fictional creations — principally Hilary Briss, Royston Vasey’s murderous butcher, whose “special stuff” in sausages causes riots; Herr Lipp, the Germanic pederast; and the hapless factory worker Geoff Tipps.

The trio are alarmed to discover that a) they are fictional creations, and also b) their creators plan to wash their hands of them and write a film set in the 17th century instead. Their inner divas kick in and they plan to terrify the League into keeping them alive. In a deliriously confusing movie within a movie, real and fictional and past and present worlds collide. The end of the world is nigh.

Gatiss and company have taken the brave step of downgrading other popular characters to cameos — including Tubbs and Edward (back, despite being killed off in the TV series twice before) and the bitchy restart programme leader Pauline. “We wanted to focus on less high-profile characters,” says Gatiss. “Some are just too bizarre to take the lead roles.”

Gatiss and Pemberton play five characters each and Shearsmith seven. (The make-up is amazing and tortuous; dental plates, body padding, even teats to widen nostrils are used.) There are cameos from Simon Pegg, Peter Kay and Victoria Wood. The plot includes a three-headed serpent, portals to other worlds and a poor serf whose job it is to clean the king’s bottom. Along with Avoca, the film was shot in Dublin, Soho and Hadfield, the Derbyshire town used for the TV series.

The big-studio, bombastic verve of the project serves to remind us just how far the League have come since meeting as students at Bretton Hall college in Leeds. The characters of Royston Vasey began life on the stage (the League won the 1997 Perrier Award). A radio show followed (netting them a Sony award; see a pattern emerging?). The TV series, which ran for three seasons as well as a Christmas special, garnered a Bafta and a Golden Rose of Montreux.

The movie has been four years in gestation and marks the tenth anniversary of the first League of Gentlemen stage show. “We worried we would not be able to do it,” Gatiss confesses. “We were nervous about falling into the usual spin-off pitfalls. We wanted to do something you can get if you’ve never seen the show before, but which, if you have, rewards your loyalty. We didn’t want to just pack them off to the Costas, like those film spin-offs of 1970s comedies.”

Pemberton offers that the League has always been influenced by cinema. “Most comedy is fairly comfortable. What we’ve always brought to our work is a sense of ambition and a sense of the unexpected.” Shearsmith adds that a film was inevitable. “Our writing has developed towards longer stories, including the Christmas special. The question was, ‘How could we make it cinematic?’” “Shaun of the Dead, which was a brilliant film, proved there was a market for anarchic, off-the-wall horror,” says Gattis, a fan of Gothic horror from an early age when he’d stay up to watch the likes of Brides of Dracula. “We didn’t want to do a retread of the TV show with all the catchphrases. We were given the chance to do a movie with explosions, time travel and monsters and we went for it.”

Gatiss plays himself, Matthew Chinnery, Royston Vasey’s vet, Briss, job-seeker Mickey, and 17th-century plotter Sir Nicholas Sheet-Lightning. He surveys the chaos at the church, including a little troupe of lichen-covered fake graves. “We all kept our fingers crossed that no-one would die in Avoca last week because if they did this lot would have to have been cleared.”

Explore Film

• Film Reviews

• Trailers

• DVD

• London Film Festival

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010