Frances Grant: Holy Grail of TV docos

How refreshing to see telly behaving rationally for a change. Prime has become the debunking channel of late, with its offerings such as Mythbusters and the excellent The Real Da Vinci Code, nicely timed if you've seen the movie version of the blockbuster novel and are poised to storm the Vatican.

The British documentary treated us to a rare experience, a show which logically and inexorably exposed a load of old tripe, in a way which didn't put down the attractions of Dan Brown's thriller but explored the reasons why you might not want to take it as gospel truth.

It seems many readers are all too willing to swallow its revelation that the Christian church is based on a 2000-year-old conspiracy to suppress women. This isn't helped by Brown's assertions that key elements are based on historical fact.

The programme was a welcome change from the breathless presentation, flimsy material repeated to the point of tedium and false climaxes of so many TV docos. Presenter Tony Robinson's quest was a fascinating look at why the myth of the Holy Grail has cast such a spell through the centuries.

He calmly tracked down the facts about those sects and secret societies which the novel claims preserved the "truth" of the Grail and took an expert look, too, at Da Vinci's famous painting of the Last Supper.

Robinson was the classic British detective, the kind of mild-mannered, dressed-to-blend-into-the-background investigator who is as remorseless as a dog with a bone.

There was no heavying needed in his extended interviews with Michael Baigent, co-author of the book expounding the conspiracy theories Brown based his novel on (this was made before Baigent lost his plagiarism case against Brown). In the end, Baigent simply had to admit that all that stuff about Jesus having a child with Mary Magdalene was, well yes, just a guess.

Dan Brown, wisely, did not front up to be exposed as the victim of an elaborate hoax. The secret society, the "Priory of Sion'," was invented by three Frenchman, one of whom was a "surrealist".

Never mind, because everyone loves an entrepreneur, someone who can make squillions with a ripping yarn which isn't, as Robinson pointed out, even very well-written. That was the only observation Robinson made about the quality of the novel. Otherwise his scepticism was neatly summed up in the nodding Jesus ornament on his car's dashboard with its sly suggestion we were firmly in the realm of the gullible and the kitsch.

Elsewhere on TV, the surreality hoaxers seem to be thriving. Entrepreneurial shows are packed with 'em, people who have grand schemes for world domination wielding weapons such as organic kids' shampoo or aerated beds. No sooner has the British show Dragons Den wrapped up a season here than we learn we're going to get our own version. Oh good.

These shows promote such edifying values, such as the Make Me a Million wannabe whose pitch to get on the show was, "I am a Tory and very materialistic and would like lots of lovely things surrounding me, which of course money would bring."

And this is what one of the show's mentors, Ivan, has to say about how the business spirit: "The passion to be an entrepreneur ... or great artist, musician or academic is equally valid, fulfilling and beautiful." Really?

Some people might think the passion to expand human knowledge or to create something of lasting beauty might be a tad more admirable than a simple desire to make pots and pots of lovely lolly selling us things we don't need. Some people might rate, Leonardo Da Vinci, say, above the creators of a new diet website.