Cameramen posing as tourists shot more than 250,000 photographs and hours of video, used by producers of Da Vinci Code prequel to get around ban on filming in Rome's churches

How do you film a movie set largely in the Vatican when the Holy See itself has banned you from shooting within its walls? If you are the producers of Angels and Demons, the prequel to the church-baiting worldwide blockbuster The Da Vinci Code, you send in cameramen posing as tourists to take more than 250,000 photographs and shoot hours of video footage.

The team behind the new film, which is based on an earlier book by Dan Brown, used the surreptitiously-gathered material to digitally recreate many of the famous papal buildings, Tuscan colonnades, fountains and monuments within St Peter's Square.

Special effects supervisor Ryan Cook told Italian film magazine Ciak: "The ban on filming put us in serious difficulty because we were not able to carry out the photographic surveys necessary to reconstruct the setting. So for weeks we sent a team of people who mixed with tourists and took thousands of photos and video footage."

The move was necessary because leaders of the Catholic church, still smarting from The Da Vinci Code's assertion that Christ married and fathered children with Mary Magdalene, had banned the film-makers from filming in or around any of Rome's churches. Father Marco Fibbi, spokesman for the diocese of Rome, said at the time: "Normally we read the script, but this time it was not necessary. The name Dan Brown was enough."

Angels and Demons director Ron Howard hinted in an interview in December on US TV show Shootout that his team had been forced into unusual measures by the ban. "We didn't shoot at the Vatican officially. But cameras can be made really small," he said.

The new film once again stars Tom Hanks as symbologist Robert Langdon, who finds himself in a race against time to stop a sinister secret society, the Illuminati, from destroying the Vatican using technology that harnesses antimatter. Ewan McGregor and Stellan Skarsgard co-star. The film is set for release in the UK and US on the 14 and 15 May.