The latest version of Anthony Shaffer's classic play will boast a script by Harold Pinter and have Caine swap roles to play the part of the bitter writer who exacts revenge on the man who cuckolded him.

Branagh came on board the project after Law, who is producing the film, sent him the script. "When Jude Law sent me Harold Pinter's screenplay and I knew that both Jude Law and Michael Caine wanted to be in it, it was the easiest decision I've ever made," he said yesterday.

"It is dark, unsettling and viciously funny. We had a script reading last Saturday that confirmed its thrilling potential. And, after working with Shakespeare and now Mozart, it's a great joy to have a genius like Pinter in the room."

Branagh was speaking to The Times at the Venice Film Festival, which was giving the world premiere of his new film, 'Magic Flute', an adaptation of Mozart's opera that is set in the First World War.

He dreams of breaking down barriers between art forms with his $27 million production one of the biggest British films shot in Britain this year. "It would be wonderful if we could get operagoers to come to the cinema and cinemagoers to go to the opera as a result of seeing the film," he said.

Although the festival takes place away from Venice, on the Lido, the festival director gave Branagh the ultimate honour of a screening at La Fenice in the heart of the city, and a reception in a 16th-century palazzo on the Grand Canal.

"It's hugely exciting to come to a place that was built in the year that the opera was written," Branagh said.

Pierre-Olivier Bardet, the film's producer, noted the irony of holding in an opera house the premiere of a film that intends to take opera away from its traditional home. "It was a kind of paradox, but it is good to have a cinema audience go to an opera for once," he said. The film - which has an English libretto by Stephen Fry was funded by the Peter Moores Foundation, the charity headed by Sir Peter Moores. Backing the production fulfilled a long-held ambition "to take opera out of the opera house" and reach new audiences. "The film had me in tears," Sir Peter said.

In setting the story during the First World War, Branagh wanted to represent "the end of an age of innocence and the beginning of a global conflict".

The opera is performed by the Chamber Orchestra of Europe under James Conlon, as musical director, and showcases a cast of rising young opera stars alongside more established performers.

The newcomers include Amy Carson, a 23-year-old fresh out of Cambridge who heard about the auditions and decided to have a go. Branagh cast her as Pamina. She spoke yesterday of being overwhelmed by working on such a production, all the more moving as Mozart also cast a young singer - a 17-year-old - in the part.

Branagh begins shooting Sleuth in January at Twickenham Studios.