The title Dan Brown used says it all. No-one in the art world calls him 'da Vinci'. That means "of Vinci"-he was Leonardo, who came from Vinci, an Italian town near Florence.

But that seems petty. Surely we can get past such minor details and see how Dan Brown's work sheds new light on who Leonardo was and the meaning of his paintings. Except that it doesn't. No-one has done more to confuse us about this intriguing 15th Century man than Dan Brown.

Robert Langdon reports Leonardo as "a flamboyant homosexual and worshipper of Nature's divine order, both of which placed him in a perpetual state of sin against God", who had "an enormous output of breathtaking Christian art" and "hundreds of lucrative Vatican commissions" (DVC 72/45).

Claims about Leonardo's sexuality are based on a couple of strands of thinking. The strongest is that he and three other people were charged with sodomy with a male prostitute when Leonardo was 24. But the charges were dismissed, and no other information about his sexuality is available. The second strand is developed from our knowledge that, as he got older, Leonardo always seemed to be surrounded by beautiful, boyish young men. However, he also had strong female friends and his male friends wrote about him as a father figure.

In short, the claim that Leonardo was flamboyantly gay is a gossipy speculation built on skerricks of information. We really can't say.

But what do we know about Leonardo's attitude towards Christianity and the church? To begin with, Langdon is quite wrong: Leonardo did not have an enormous output of Christian art (in fact, he found it difficult to finish anything past the sketch stage). Nor did he receive huge commissions from the church. In fact, only late in life did he work under one Pope, Leo X, and then he was mainly inventing rather than painting.

Once again, the so-called facts that Dan Brown promised just don't add up.

But could Leonardo have been covertly communicating a new religion through his artwork? As Grand Master of the Priory of Sion, could he have secreted away in his paintings what he knew about the true nature of Christianity?

No art scholars seem to think so.

While The Da Vinci Code makes a lot of the feminized figure on Jesus' right in Leonardo's The Last Supper, art critics all agree that this is a normal way of depicting saintly men, as the disciple John was. And while Leonardo's diaries suggest that he wasn't a conventional Christian believer, nor do they suggest that he was devising and painting out a new religion of sacred femininity. And the Mona Lisa, while intriguingly androgynous in appearance, cannot be a means by which Leonardo was trying to explore a new sexuality. The novel claims that the name is an anagram of two Egyptian deities of fertility. But art history tells us that Leonardo did not even name his painting-it was named later by one of his biographers!

Speculation mounts on speculation, until we readers feel convinced that Leonardo must have been up to some strange religious games. But when you pull apart the claims, there is no evidence to back them up.

And without that evidence, we would be foolish to develop a new religion out of the fanciful utterances of a poorly informed character in an airport novel. Wouldn't we?