I’VE come to see a man about a mystery – the mystery of who exactly Alexander Gardner was. Was he one of the greatest explorers of the 19th century, a heroic Scots-American who became the first white man to explore vast areas of what is now India and Pakistan, or did he, as some believe, just make the whole thing up? Was he Scotland’s Marco Polo or Scotland’s Baron Munchausen?

From the evidence I’ve seen so far, the answer is not entirely clear, although from the pictures of Gardner that have survived, it’s obvious that he was far from an ordinary person. In the most famous photo of him, he is sitting legs akimbo, in a vivid tartan suit complete with tartan turban. He’s also sporting a gigantic beard which hides the fact he has a great sword wound across his neck. This man has been in the wars, and some of his story is grim, dark and unpleasant. But how much of it is true?

The man I’m hoping will be able to answer that question and a few others about Gardner is the historian, writer and broadcaster John Keay, who I’m meeting at his flat in Edinburgh. Keay made documentaries for BBC radio for many years but is also known for his writing on India and the east, and his most recent project is a book about Gardner, The Tartan Turban. The book is, he says, his chance to do what he can to finally provide a definitive answer to the question: was Gardener a great man or a fantasist?

Keay, who is 75, tells me he was wary about tackling the subject of Gardner when he first started the book. “The last work that had been done on him was in the 1920s,” he says, “and I was inclined to be very cautious about him. His travels were probably the most remarkable in the whole of history of travel in the early 19th century – he covered an enormous amount of ground in central Asia on his own but people have been very suspicious and think he may have invented them or based them on hearsay.”

The facts - according to Gardner – are these. He was born in America to a Scottish doctor and a mother who was half Spanish and half Aztec. In 1817, he left home to sign up for the Russian army but instead went wandering in central Asia, where, it is said, he fought off a pack of wolves, and discovered great stone horses standing in the desert and forgotten temples. Five years later, he was in the employ of a prince fighting for the throne of Kabul in Afghanistan; he was also married to a native women, who was later murdered by enemy forces. Gardner then fled to the Punjab and became a commander in the army of the Maharaja. As a soldier for hire, he also worked for the vizier of Lahore who ordered him to punish a man by cutting off the man’s nose and hands, which Gardner did, marking him out for many as not only a fantasist but a brutal man capable of doing anything for money.

Keay says much of the detail of this extraordinary account is fuzzy to say the least, but in writing his book he has made progress in adding flesh to the bones. “I don’t think anyone will ever totally authenticate and vindicate his story but we’ve gone a long way in this book,” he says. “I am more or less persuaded that he did to go to most of the places he said he claimed to have been”.

Keay also points out that when Gardner was telling his stories of adventures, he was an old man and was remembering back 40 years. “We should give Gardner due credit for what I think he did do, but we should also keep an open mind about certain aspects of his life. I’m probably about the same age as Gardner was when he was telling his story and when I try to think back to what I was doing 40 years ago, well, you know, there are more gaps than anything else and you tend to invent things. There’s a nice line from Disraeli – “like all great travellers, I have seen more than I remember and remember more than I’ve seen.” The fact that I have this long perspective now makes me more sympathetic to his story than I would have been in my 20s or 30s.”

So where does John Keay’s perspective come from? He was born in Ilfracombe in Devon to a Scottish father, master mariner Stanley Keay, and English mother Florence Keeping, but has lived most of his life in Scotland – he currently lives in Edinburgh and Argyll. At university, he read modern history at Magdalen College, Oxford, where one of his tutors was the writer Alan Bennett, whom Keay remembers being bored by the whole process of teaching.

“He was my tutor for medieval history,” he said. “It seemed to bore him as much as it did me. I don't think I'd count as one of his History Boys. He also provided coffee made with milk in a saucepan on his single electric ring. Quite disgusting.”

After university, Keay visited India frequently and it was there that he decided on a career in writing, sending articles about the region to many British newspapers and magazines. He then joined The Economist and started contributing to BBC Radio; his first book, Into India, appeared in 1973.

Much of the rest of his writing has also been about India through its great empires and the British colonial period. I ask him if, as a historian, he detects a whiff of old-school British imperialism in the antics of the Brexiteers? “It’s an English imperialism, not a British imperialism, and I have absolutely no sympathy with them whatsoever,” he says. “I think it’s an English phenomenon and it didn’t surprise me at all that Scotland voted to stay in Europe. We did play our part in the empire but the belief in the empire was never that strong in Scotland. It was a good deal and a good way of rescuing family’s fortunes or whatever – it was a great opportunity but I don’t people much thought of it as a Scottish empire. Scots did very well out of it, but I don’t think they had proprietary feelings about the empire in the way that the English did. The English thought ‘this is our empire’.

Keay adds that he is just as horrified by Trump as he is by Brexit. “The thing about democracy is that you have to accept that every now and then an election is not going to go the way you wanted or expected and you’re going to be lumbered with a liability. It’s easy to imagine someone like Trump turning into a Hitler. I don’t think that’s hysteria – in a way, the horrific thing is he’s so totally confident and yet is so inexperienced and ill educated.”

In some ways, there are similar factors at play with Gardner – certainly, to many he seemed boastful and self-centred but, after completing his research, Keay sees him in a more benign way, living in Kashmir, dressed in tartan and telling his stories to visiting tourists. Even the horrific stories about the bloody punishment he handed out on behalf of one of his employers, chopping off the man’s hands and nose, has to be seen in the proper context, says Keay.

“Gardner says he had little choice in matter – but he took on the responsibility of judicial mutilation, cutting off a man’s ears and nose and hands. Very soon after, the sikh empire was overrun by the British and when they heard about this so-called American who had inflicted this appalling punishment in cold blood, they were horrified. So Gardner was not only written off as a fantasist but a thorough scoundrel and a nasty piece of work. He says he did it because he was in fear of his own life and of his men. He was scared for his own life and had no choice in the matter – and you can take that or leave it.”

Keay’s decision is to believe it and see Alexander Gardner as a man whose stories may have become muddled at best, but who ultimately deserves to be seen as a traveller and adventurer in the same league as Marco Polo and the greatest explorer of the early 19th century. Some say Gardner’s life was too outrageous to believe; John Keay says the stories are so outrageous they must be true.

The Tartan Turban: In Search of Alexander Gardner is published by Kashi House at £25