Ancient stone carvings confirm that a comet struck the Earth around 11,000BC, a devastating event which wiped out wooly mammoths and sparked the rise of civilisations.

Author and historian Graham Hancock made this argument in his book Magicians of the Gods. This interview with Hancock was originally published in October 2015.

When I eventually reach Graham Hancock's house, I am late and out of breath. The amateur archaeologist lives in a grand slab of a place halfway up one of Bath's lung-busting hills and I have been struggling with a bag full of his bestselling books.

The 65-year-old opens his imposing front door, waves away my apologies, and ushers me straight down to his study, which is spilling over with books and expensive-looking curiosities. He offers me a cup of coffee and enquires about my journey. He is avuncular and chatty – not at all the wild-haired eccentric my research had led me to expect.

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Is the Great Sphinx of Giza many thousands of years older than the Ancient Egyptians? Credit: Santha Faiia

Twenty years ago, Hancock set the cat among the academic pigeons when he published a book called Fingerprints of the Gods, a re-evaluation of mankind's past that claimed an advanced civilisation was wiped out by a giant comet towards the end of the last Ice Age.

Based on Hancock's own investigations and interviews with archaeologists and astronomers, the book claimed survivors of this cataclysm, the giant flood remembered in myths all around the world, went on to settle in locations from Mexico to Egypt and impart their ancient knowledge to the other remaining humans.

Among the most attention-grabbing claims in the book were: a suggestion that the Pyramids of Giza were designed to store books of knowledge written by an ancient civilisation; that the Great Sphinx preceded the Ancient Egyptians by many thousands of years; and that Plato, who wrote about Atlantis in his books Timaeus and Critias, knew exactly where the fabled lost city was hidden.

The book was an instant hit and has, to date, sold more than nine million copies around the world. Hancock, a former East Africa correspondent for The Economist, went on to present two documentary series on Channel 4, became a popular lecturer in "alternative history", and built up a strong fan base online.

Now, he has written a sequel to Fingerprints, Magicians of the Gods, which reveals "explosive new evidence" to support his claims. It also warns of another comet strike that is destined to hit Earth in 2030.

The book, which is already a bestseller, has proved irresistible to fans and Hancock's talks, which he has been holding to accompany the launch, have been hugely popular, attracting far larger audiences than equivalent talks by Booker-prize winning authors.

What Hancock has not achieved, however, is credibility. Leading archaeologists have been denouncing his theories for decades. He has been compared to The Da Vinci Code author Dan Brown and dismissed as a pseudo archaeologist or "Pyramidiot". The organisation for whom he is delivering a talk on October 15 - the "mind, body and spirit company" Alternatives - also hosts events about ghosts, clairvoyance and the paranormal.

Graham Hancock studying ruins near Cuzco in Peru Credit: Santha Faiia

Hancock has no formal qualifications in archaeology, history or astronomy. His long-standing interest in hallucinogenic drugs – "they are something that society really needs" – has not enhanced his reputation either.

But the author says he has never claimed to be an academic. He presents himself as a journalist who is simply reporting theories by scientists who think they can fill in some of the gaps in the history of mankind – holes acknowledged by all mainstream academics.

"Let's get to grips with that first of all," he says. "The foundations upon which history is based look increasingly suspect. Let's no longer shroud ourselves in the illusion that [mainstream] historians and archaeologists are invincible."

There are, according to Hancock, two smoking guns. Firstly, naondiamonds - types of diamonds that result from a cosmic impact - were discovered recently in North America. In 2014, the Journal of Geology confirmed that this matter was formed 12,800 years ago.

"For someone who proposed [in Fingerprints of the Gods] a giant cataclysm between 12,000 and 13,000 years ago, it is a bit of a gift from the universe to have a bunch of very major scientists now saying that there was indeed a giant comet impact 12,800 years ago," he says.

Secondly, excavations at an archaeological site in Turkey called Göbekli Tepe have uncovered ruins that are at least 11,600 years old. That is more than 6,000 years older than other megalithic sites such as Stonehenge. A civilisation capable of the advanced architecture and art discovered at Göbekli Tepe is not supposed to have existed 11,600 years ago.

So what is the explanation?

"We're looking at a place where the survivors of a lost civilisation settled." References to these survivors – described as sages, magicians or "mystery teachers of Heaven" – can be found in various cultures, he adds.

"When the evidence started to build up, my first feeling was one of weariness," he says. "Because my books have been quite successful, I have been subjected to more of the scathing and withering attacks on the quality of my work, and on my qualities as a human being, by the academic community than anybody else. But this story needs to be told. It would just be plain wrong for me to ignore it."

Do the attacks bother him?

Could a comet be on a collision course with Earth? Credit: Alamy

"I certainly don’t relish them but I don't resent them either," he replies. "If you put out an extraordinary reinterpretation of the past then you can expect those who have invested their entire careers studying the human past to say 'hang on a minute'."

And Hancock believes another chapter in the history of the human race is about to come to an end. In the conclusion to his new book, he writes: "It is possible – indeed highly probable – that we are not yet done with the comet that changed the face of the earth between 12,800 years ago and 11,600 years ago."

There remains, he explains, at least one large comet in the same meteor stream. In 2030, we are due to come into contact with it once again.

"We have fallen out of harmony with the universe… In mythological terms, we tick all the boxes for the next lost civilisation," warns Hancock. "Plato says it very clearly about the citizens of Atlantis: there was a time when they loved a pure and good life but they became arrogant and cruel and no longer bore their prosperity with moderation. I think we sound a lot like that."

Is Hancock really suggesting that the universe is going to punish us in 2030 for our immoral society? That seems an outrageous claim, even by his standards. He leans forward and looks me directly in the eye: "I'm saying that that is what the ancient traditions suggest."

Magicians of the Gods: the Forgotten Wisdom of Earth's Lost Civilisation by Graham Hancock (Coronet, £20) is out now