'It's odd that invoking the possibility of alien influences should itself be a sign of madness,' he says. He doesn't believe in Von Daniken's intergalactic missionaries, but chides me for making fun of them. Hancock's first 'mystery' book - a quest for the lost Ark of the Covenant - was The Sign and the Seal in 1992, and he seems to see himself as an Indiana Jones figure, kicking against the constraints of academia, thinking the unthinkable. I'm not aware of any current which is about radically changing the model. It's not about changing the model radically. There is a model of how the past is and a lot of academic archaeology is about refining the model. I'm a writer, communicating ideas to the public. 'I'm not an academic I'm not an archaeologist. The 51-year-old former journalist pleads not guilty on both counts. The other is that I'm a rather sinister fellow who is misleading the public.' One is that I'm a lunatic-fringe train-spotter with an absurd enthusiasm for something ridiculous in the past. 'It seems that people talk to me with a preconception about what I am,' he says, 'and then whatever I say or do doesn't make any difference.There are several preconceptions. But, undeterred, he is back with another Channel 4 series and a vast tablet of a book, called Underworld, that attempts to provide the evidence for his lost civilisation.

In 1999 the BBC's Horizon did a demolition job that was applauded by archaeologists and assorted Hancock-haters. His arguments were treated with derision. It was restated in Heaven's Mirror, a glossy book produced to coincide with a Channel 4 series in 1998. He first expounded the thesis in 1995 in Fingerprints of the Gods (the echo of Erich Von Daniken's pro-alien Chariots of the Gods is unfortunate). Hancock has spent the past 10 years writing books and producing TV programmes which argue that everything we are told about ancient history is wrong: civilisation didn't start in Sumeria and Egypt around 3,500 BC it began 10,000 years before in great cities which subsequently suffered a cataclysm. But his critics would say appearances deceive: he is either a lunatic, a charlatan, or both. Graham Hancock doesn't look mad as he sprawls in an armchair in his small, neat house in Kennington, south London.

Underworld by Graham Hancock