The decision by Sister Mary Michael, 61, to subject herself to the ascetically demanding Lough Derg pilgrimage in Donegal is just the latest testament to the passions being aroused against the book in the Catholic community.

Sony Pictures, the studio behind the film, has consulted religious experts on how to avoid causing offence to Catholics and other Christians over controversial storylines, such as the claim that Jesus married Mary Magdalene and that she bore him a child.

The Opus Dei movement is particularly concerned at the depiction of the novel’s main villain, a murderous albino monk called Silas. Opus Dei does not have monks and, as an organisation, advocates a peaceful, Christian life of hard work far removed from the ruthless skulduggery that takes place in The Da Vinci Code.

Sister Mary, a former Discalced Carmelite who now belongs to Our Lady’s Community of Peace and Mercy in Lincoln, led the protesters who greeted Tom Hanks, the Hollywood star, as he arrived at the cathedral to shoot the book’s climactic scenes.

Lincoln is being used for filming this week in spite of its own dean branding Dan Brown’s multimillion-selling book “a load of old tosh”. The Very Rev Alec Knight said that the story was “balderdash”. He and the cathedral chapter agreed to let filming take place after the film’s producers made a £100,000 donation.

The cathedral is serving as a double for Westminster Abbey, which refused to take part in the making of the £53 million blockbuster.

Other scenes are being filmed this summer at Winchester Cathedral and Rosslyn Chapel, near Edinburgh. Filming has already taken place at the Louvre in Paris.

Hanks, who plays Robert Langdon, the hero of the tale, will be in Lincoln for just two days. Yesterday he was chauffeur-driven the few dozen yards from the five-star White Hart hotel in the city to the cathedral. Looking tired, he waved to autograph-hunters but quickly disappeared inside the building with his director, Ron Howard, and co-star Sir Ian McKellen.

Sister Mary, robed in brown habit and blue veil, told The Times that the central thesis of the book was drawn from an old gnostic heresy that she first became aware of 50 years ago, when she was 11. She admitted that she had not read the book but said that she had read enough about it to understand its central errors.

She accused Lincoln Cathedral of the sin of simony, conducting financial transactions involving spiritual goods.

“The Church should not be accepting money for something that is not a true story,” she said. “There is something wrong. They really should be praying more, and then the money would come in. I do not believe the film will be successful. The essence of what I believe is that I received the true body and blood of our Lord at Mass this morning. That is the true bloodline.

“To a believer, any believer, what is happening is blasphemous. It is an offence against God. I am not going to bash anyone over the head with a Bible, I am just trying to make reparation to God.”

She said that many other Catholics in the city opposed the book but conceded that the protest had been small. “It takes a bit of courage to do this. Most people have decided to pray at home.” The scenes in Lincoln are expected to take five days to complete.

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