It was the late '70s and the Lancaster-born, Burnley-raised Stewart was becoming increasingly aware of the fact that his face didn't quite fit at the Oxbridge-heavy Beeb.
"It was very elitist and I kind of railed against that," explains Stewart. "In my annual review, I said to this HR chap that I'd like to work in current affairs and he said 'if you're one of those bright-eyed young things who wants to work on Panorama, you've got no chance'.
"Unfortunately, that's exactly what I wanted to do!"
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Stewart himself describes his childhood as 'somewhat unusual'. Born in Lancaster in 1950 to a single mother in a strong Irish Catholic community, even his conception was a point of controversy. "My mother was quite a senior nurse at the time, so I think it was a bit embarrassing that she should be pregnant," says Stewart. "She kind of disappeared for a year.
"When she reappeared, she had a little baby and I think the word was 'I'm back, I've got a baby, and it won't be spoken about again'," he adds. "She brought me up on her own and we moved house a lot as she tried to get settled, so it was a pretty miserable time for me from memory."
Hopscotching across Burnley from school to school in his youth, Stewart admits that he was a poor scholar who struggled to read in his early years, only taking to academia once he attended secondary school at St Theodore’s (now Blessed Trinity).
"At best, we were studying to become engineers and hoping to land apprenticeships, but I got lucky in that I met grammar school boys from the bilateral year below me who were interested in more than just beer and football, which was good for me," he says. "After that, my teachers at college took me under their wings and changed my life. I became an academic."
Studying Politics & Modern History at Lancaster University before heading south to do a Master's in International Relations at the University of Sussex, Stewart then returned to Lancaster to complete his doctorate in political behaviour. He had well and truly fallen in love with the 'lifestyle and ambiance' of university.
"It was the 'anything goes' liberal '60s and, to be honest, we had it easy, so it was a dream," he explains. "I didn't want to leave because academia seemed easy. Teaching eight hours a week and then spending most evenings in the pub? Brilliant. But I realised it was a false existence. I just didn't have the dedication other academics had to research and their subject."
Aged 24 at this point, he landed a position in the BBC s Audience Research Department to work on a study on the influence of the media during the 1975 United Kingdom European Communities membership referendum. It was after the study was concluded that he had his fateful encounter with the aforementioned HR boffin.
"The BBC didn't take people at face-value, so I thought 'let's do something decent for a change instead of being selfish and swanning around universities in the BBC'," says Stewart. "So I became a teacher. I enjoyed it; this was pre-Thatcher, so teachers enjoyed a prestige in the community. Those were good days and I rose quite quickly in the school ranks.
"I was deputy head in my mid-30s and, suddenly, I realised both me and my wife, who was on the same career path, could be head teachers and retired by 60 in suburban London," he adds. "I didn't fancy that, so my mind started to wonder about other things and kept coming back to documentaries.
"I had itchy feet."
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Over the next 40 years, Stewart taught; joined the army; left the army; returned to teaching; pitched a sports documentary to the BBC through former Welsh rugby union player-turned BBC executive Cliff Morgan; produced one of the longest-running football magazine shows on TV; made official documentaries for the Olympics, FIFA, and Tiger Woods; and wrote a dozen books.
'Itchy feet' doesn't quite cover it.
It all started with his love of sports. In 1985 and still working as a teacher after returning from a couple of years in the army - 'a growing-up experience', as he puts it - Stewart submitted a treatment to the BBC for the definitive documentary on the history of sport. A few days later, sat in his office, the school secretary buzzed through to tell him someone from the BBC was on the line.
"This voice just said 'Hello, I'm George Carey'," says Stewart. "I knew who it was - this was the chap who had founded Newsnight and who they called 'Two-Brains Carey' because of how terrifyingly bright he was. He asked if I could come in for a chat and I just replied 'Yeah; when, tomorrow? That was that, off I went back to the BBC."
While the sports documentary never got made with the BBC due to funding issues, the pitch got Stewart's foot in the door and he was soon working in current affairs as he had always dreamed of. It was at this point that he got wind of Trans World International's intentions to launch a sports anthology weekly magazine show called Trans World Sport.
"I got recommended for Trans World Sport in 1987 because of my passion for the internationalism of sport," says Stewart. "What fascinates me is the wonderful kaleidoscope of sport, from sumo to Aussie Rules, so it was a dream project to work on. It made my career and, because of how well it did, I was given carte blanche to develop things."
Stewart went on to found the Olympic Games Camera of Record in 1994, documenting the magic of the Games in a behind-the-scenes style at events from Lillehammer 1994 to Athens 2004, and produce 'The People's Game', FIFA's official history of football; the IOC's official centennial documentary 'Olympic Century'; the official history of Wimbledon; and Tiger Woods' official biographical documentary 'Tiger'.
He even got to finally make his documentary on the definitive history of sport, titled 'Blood, Sweat and Glory'.
"My passion is storytelling," says Stewart, who developed his love for documentaries through watching BBC programmes as a child. "I'd always been moved by documentaries, so I knew I wanted audiences to feel something; to enjoy, be horrified, be excited. That's where the thrill is for me."
Having grown up during the Kennedy presidency and the civil rights movement, Stewart had also cultivated an intense passion for history over the decades - a passion he was able to explore and nurture further by producing a number of historical documentaries including 'Britain at War in Colour', which won him a BAFTA and a Grierson Award, and the ‘Second World War in Colour’ series, which won him a Peabody.
"Looking back, having been an academic, a teacher, and a soldier, I was used to dealing with detail to better portray a bigger picture," says Stewart, whose eye for narrative has earned him a reputation as one of the country's premier documentary film-makers. "To be able to come full-circle to the kind of visual storytelling I'd been passionate about as a kid was great."
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These days, it's the written word which occupies Stewart most pressingly.
A prolific author, he has written seven historical novels since 2011 and five books of historical non-fiction, the latest of which is titled Barbarossa. Focusing on the story of the battle for the Eastern Front during the Second World War, the book was published in April ahead of the 80th anniversary of Operation Barbarossa in June.
Having been travelling to the Soviet Union and Russia since 1969, Stewart has gained a unique perception of the country over the decades and resolved to write the first Western account written from the Soviet Eastern European perspective on the bloodiest military campaign mankind has ever known.
"It was all about finding real experiences from people who were there to guide the narrative," explains Stewart, with Barbarossa drawing on never-before-seen material and witness accounts. "First-hand accounts which offered a unique and never before properly-explored take were the inspiration for the book.
"The project as a whole was rewarding, but the horror and the catalogue of brutality was extraordinary," he adds, with the Barbarossa campaign having seen four million Nazi troops march on Moscow leading to over 40 million deaths. "It wasn't an easy book to write because you soon realise the kinds of creatures human beings are.
"But the Eastern Front is where eight out of every 10 Germans died; it's where the war was won," he adds. "The heroism, resolve, and courage on show..."
With plans for further books bubbling away in the back of his mind, Stewart is far from finished, his passion still burning bright. "Because I had an auspicious beginning to my life and was a bit of a lost cause, I've never believed talent is something people are born with," he says. "If you're passionate, work hard, and have a bit of luck, you can do something special."
Oh, and another thing. During his second stint with the BBC, he did eventually get to work on Panorama. "I never did get to meet the guy who said I'd never manage that, though!" he says with a laugh.