LIKE the spies who lurk in it, you can’t really trust what you know about The 39 Steps. Remember that erotic moment in which Richard Hannay’s female companion removes her stocking while handcuffed to him? Not in the book - Alfred Hitchcock made it up for his 1935 film. Or the moment Hannay hangs from the clockface of Big Ben to defuse the timer on a bomb? Not in the book either - that was Robert Powell in the ‘78 film. The 39 Steps may be one of the most successful novels of the last 100 years and the daddy of a whole genre of thrillers and spy novels, but its fame is built largely on the films.

The fame of the man who wrote the book is just as complicated. When he died in 1940, John Buchan was given a state funeral and was revered as a novelist, scholar, politician, publisher, war correspondent and imperial proconsul, but, as with many other great Victorian figures, there has since been a reassessment. Was Buchan just a “Scotsman on the make” out to use his connections to get on? Was he anti-Semitic? Was he racist? His granddaughter Ursula Buchan has set out to give her answers to those questions in a new biography Beyond The 39 Steps and, as the title suggests, she also wants to remind us there was more to John Buchan than his most famous book.

One of the most surprising episodes in the new biography is Buchan’s experiences in the Gorbals as a child. If we think of Buchan, we probably think of him as a slightly grand Victorian figure, but his childhood was anything but. His father was a minister at the John Knox Free Church in the Gorbals and John went to school in the area, at Hutcheson’s on Crown Street, where he came to know the population and their problems. Many years later, he featured a gang of Gorbals schoolkids, the Diehards, in one of his novels, Huntingtower, and Ursula Buchan is convinced his time in Glasgow’s most notorious slum had a profound effect on him.

“It had a huge influence,” she says. “Though Huntingtower, which is the first book where the Gorbals Diehards appear, doesn’t come out until the 20s, he’s remembering his walking through the Gorbals to school every day. And, also, when he went to Glasgow University, he walked everywhere so this was the Glasgow he knew and of course because his father was a minister in the Gorbals, he was brought up knowing about what it was like to be poor and I think that was huge for him. He never forgot it and it was one of the reasons he could get on with anybody – he could walk with kings but never lost the common touch.”

The other extraordinary thing about Buchan’s time at Glasgow University, and then Oxford, was his capacity for work – something that never left him. He was studying for a classics degree, but he was also writing short stories, articles for The Glasgow Herald about what it was like to be a student, and a history of Brasenose College. A journalist at the time noticed Buchan and called him a “miracle of precocity”. Mind you, the journalist also said that there was no sign that he would ever do much in fiction.

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To be fair, that was pretty much true until The 39 Steps was published in 1915 when Buchan was 40. It was an immediate success and even now, 100 years on, you can see why: Hannay is hugely likeable, the prose is pacey, and Ursula Buchan believes the modern novel of espionage would not have developed along the same lines without it. Certainly, both Graham Greene and Ian Fleming acknowledged their debt to him.

However, Ursula Buchan does get slightly frustrated that the story of her grandfather has become pretty much all about The 39 Steps. “That’s why I called my book Beyond the 39 Steps,” she says. “I knew I had to have it in there somewhere but he wrote that book in six weeks when he was ill to amuse himself because he’d run out of thrillers. He never made any literary claims for it, but he realised he could make some money.”

Ursula Buchan believes her grandfather’s real legacy lies in the fact that he lived a good and useful life and says she has tried her best to emulate it in her own work as a gardening journalist and writer. But just look at the list of what he did and you can see how hard that would be: he wrote more than 100 books, he was an MP, he was a publisher in Edinburgh, he was Governor General of Canada, he worked as a journalist during the First World War and wrote a 24-volume history of it. He also worked as an administrator in South Africa on improving the conditions in the concentration camps that had been set up by the British Army to accommodate Boer prisoners. The conditions at the time were a scandal and Buchan managed to get the death rate down by improving sanitation and water supplies.

“People don’t understand that the concentration camp in South Africa is not the same as an extermination camp in Germany,” says Ursula Buchan, “but they weren’t nice places and when the civil authorities took them away from Kitchener and the military, they were absolutely horrified by the death toll. The army weren’t, I don’t think, actively cruel but it’s not what armies do – they don’t know how to look after civilian populations.

“By the time John Buchan got there in October 1901, there was already deep disquiet in Britain. That was what impelled them to turn it over to the civilian authorities and really try and do something. And they did. Within six months they had cut the death toll substantially and the protests in Britain died down.”

Ursula Buchan says her grandfather’s approach to the camps was typical of his pragmatic views. “He was not a jingoist,” she says, “and he worried the Empire, if clever energetic and public-spirited people didn’t continue to be involved with it, would decline to the detriment of everybody. In some ways, he was very much ahead of his time.”

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In other, more controversial ways of course, he was very much of his time and Ursula Buchan acknowledges this of her ancestor: his occasional use of the n-word, for example, or his use of language, mainly in The 39 Steps and the other Hannay books, that would now be considered anti-Semitic. His granddaughter points out that there are favourable depictions of Jews elsewhere in Buchan’s work; he also supported the Balfour Declaration and in 1933, less than three months after Hitler came to power, he was one of only 50 MPs who signed a motion deploring the treatment of Jews in Germany.

“Those were different days,” says Ursula Buchan, “and we have to be very careful about wagging a disapproving finger because if we do that, we don’t allow ourselves to understand people in earlier times. We put a distance between them and us – ‘they use the n word, they’re deplorable, I’m not going to connect with these people’. It’s very interesting that nobody criticised him at the time because everybody was using the same language – they generalised about peoples and races in a way that we’re very much more reticent about.”

Ursula Buchan also has a warning for Scottish Nationalists who might seek to claim John Buchan as one of them, based mostly on his famous statement “every Scotsman should be a Scottish nationalist”. In fact, Buchan was a “unionist nationalist” who supported Scotland’s place in the British union and Ursula Buchan is clear about where his loyalties lay. “I don’t think he would have supported the modern Scottish Nationalist Party,” she says firmly.

As for Buchan’s Scottish background, his granddaughter says it is the key to understanding him and that the memory of his minister father with his poor, shabby congregation scattered round inner Glasgow influenced him hugely and drove him to push himself. Ursula also laughs about him being a hard act to follow. She never met her grandfather but having him as a relative, she says, meant writing was always considered a good and worthy thing to do.

Ultimately, she would like to encourage people to read some of her grandfather’s lesser-known works and find some of the gems embedded there. Such as this one about the fragility of civilisation: “There is a narrow line between the warm room and the savage out-of-doors … You call it miles of rampart; I call the division a line, a thread, a sheet of glass”.

And this one about his fears for the consequences of scientific development. Everybody in the future will be comfortable, he said, but easily distracted. “Their shallow minds would be easily bored,” he said, “therefore unstable. Their life would be largely a quest for amusement.” In other words, John Buchan predicted the effects of the internet. It seems there was no end to his genius.

Ursula Buchan is appearing at Aye Write at the Mitchell Library in Glasgow on March 17 at 1.15pm. See for more details. Beyond the Thirty-Nine Steps is published by Bloomsbury on April 18