Still no nearer the Deep Throat truth.

That Linda Lovelace became "the new sex goddess of the 70s" due to an ability to perform a special kind of oral sex was remarkable enough. Even more mind-boggling were events that followed and form the core of Mark Kermode's documentary. By the end we are none the wiser as to the truth, the whole truth and nothing but the truth as two people, Lovelace and her ex-husband/manager Chuck Traynor give different accounts of the same story.

Both are now dead, although that's not the reason for a failure to establish whether Lovelace was the star or the victim of the sorry scenario. She died in a car accident earlier this year, but can be seen giving her account in TV interviews and excerpts from her books. Traynor died of a heart attack shortly after filming an interview for the programme putting his side of events. The documentary cuts back and forth between the two relating the whole sordid story.

Even in the post-watershed slot we are allowed only a few fuzzy glimpses of Deep Throat, the 1972 movie in which Lovelace played a woman with a clitoris in her throat. What was different about the film, and helped ease hard core porn into the mainstream, was the audience. Instead of men in dirty macs, married couples, celebrities and UN delegates went to see it in New York. It became fashionable to go to see porno movies in America.

Lovelace was paid $1,200 for six days work on Deep Throat, seen by a quarter of a million people during the New York run. More people knew who she was than Dr Kissinger, whose international diplomacy was no match for a woman performing oral sex.

The twist came two decades later when Lovelace, who'd been living as a wife (having ditched Traynor) and mother, claimed she'd been forced to take part in the movies at gunpoint and how Traynor regularly beat her up. She campaigned against pornography and championed the women's liberation cause. Traynor denies the abuse, while admitting that "I wasn't a pleasant guy when I was mad, but I wasn't mad long". His history running a topless bar and allegedly organising for Lovelace to be gang-raped hardly endear him to you.

Then again, it's difficult to reconcile Lovelace's accusations with the woman who, in the late 1990s, appeared at conventions signing video copies of Deep Throat and then posing for a men's magazine. Kermode admits it's impossible to know who's lying. Hardly a satisfactory end, but a good story all the same. You can only wonder why it hasn't been turned into a movie already.