Last year, Johnny Ball was skiing in France, wrapped up against the cold with only a small strip of his face visible between goggles and scarf. But that didn’t stop the man next to him turning around and, on the strength of four or five muffled words, crying with childlike glee, “Johnny Ball!”

“People have memories like elephants,” says Ball, whose hugely popular, long-running Think programmes made maths and science fun in ways even the coolest teacher could only dream of. “A few years ago I was filming at Brighton Racecourse and two guys came up to me – they’d had a few, it’s fair to say – and one said, ‘Johnny Ball, I’m a nuclear physicist because of you’. And his mate put his arm around me and said, ‘and you influenced me, too – I’m a bookmaker!’”

If it hadn’t been for the 1953 FA Cup Final between Blackpool and his hometown side, Bolton Wanderers, this week’s TV Hero would probably have been the (frankly disappointing) Graham Ball. “The right-back for Bolton was Johnny Ball, so at school they made me play right-back and called me Johnny,” he explains. “Which was terrible – I wanted to be a centre-forward! But I liked Johnny, and it stuck.”

Despite these Lancastrian credentials, Ball was actually born in Bristol. “My parents moved to Bolton when I was 11 – but I found them,” he wisecracks (at 77, Ball is still very much the joker). It is to this upheaval he attributes the surprising fact that one of TV’s most famous eggheads only left school with two O-levels.

“In those days, a Bristol accent in Bolton was like a foreign accent,” he says. “I was very strong in primary school. But at grammar school in Bolton I went from 2B to 3C, 4D, lower 5E and finally 5E, because they didn’t have a 5F. I just fell downstairs – my education just collapsed. So I left with 2 O-levels – but I got a hundred per cent in maths.”

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He later acquired three more O-levels on his own initiative, and was working towards becoming an industrial accountant until called up for National Service. Opting to do three years so he could choose his own trade, he became an RAF radar operator in Wales, where he was happy to find himself “among boffins”. Then he was posted to Germany where, among other things, he wrote and produced his first pantomime.

On being demobbed, he returned to Wales to work as a Redcoat at Butlin’s in Pwllheli. “That was my training,” he says. “It’s smile school, basically. Everyone was there to have a good time, and everyone was happy.” True to the showbiz traditions of the era, he then honed his stand-up comedy skills on the northern club circuit. “It was a bullfight, but rough nights were thankfully few and far between. I was actually very good at it.”

Early TV exposure, though, proved to be less of a big break than a painful fracture: an appearance on The Val Doonican Show, dogged by technical problems, and for which his agent had persuaded him to miss rehearsals so he could do shifts in a pub, saw Ball die a very public death in front of 19 million people. “It was a terrible disaster,” he groans. “I definitely knew I had to change tack after that.”

Changing tack meant going along for an interview for what he thought was Crackerjack, but turned out to be Play School. Which is how Ball found himself playing in the dressing-up box alongside Humpty, Hamble, Big Ted and co on the enduring pre-school favourite.

“After about 10 minutes, I knew I’d got the job. They said, ‘You’re going to be great in Play School’ and I said ‘What’s Play School?’. They told me it was on at 11 o’clock in the morning on BBC2. Nobody had BBC2! I didn’t want to do it, and after three weeks of programmes the producer said, ‘If you’re not going to take it seriously, we won’t keep you on’. I thought, why am I being bad at this? So I changed tack, and I loved it.” He ended up staying for 16 years. “It was really me hiding away while I learned about television.”

Off screen, Ball was a regular writer for Brian Cant’s Playaway, while also providing gags for the likes of Dave Allen and Les Dawson. When the chance came to front his own show, he suggested a series of monologues in which he could combine his stand-up comedy training with his passion for maths, science and technology.

Launching in 1978, Think of a Number ran for six years, in parallel with five series of sister show Think Again, and continued in various guises all the way up to the last edition of Johnny Ball Reveals All in 1994. The programmes earned him numerous awards, including a Bafta and even an Emmy nomination. Perhaps surprisingly, Ball insists they were never intended to be educational.

“It was designed as entertainment,” he says. “I didn’t even use words like diameter or circumference for a circle – I said, ‘this is across it, this is round it’. I never used jargon – apart from once, when I said, ‘this is a polygon,’ then threw it away and said, ‘you see: poly, gone’. It was about communicating. I’d done 12 years in the clubs, where you have to learn to communicate with absolutely any audience.

"Because I’d only got two O-levels, everything I put in the shows I had to research myself,” he adds. “It made the hair on my neck stand up when kids said, ‘I’m going to be a scientist because of you’.”

Of course, it has since emerged that the BBC during this era wasn’t quite the clean-cut ‘Auntie’ of popular repute. In a 2012 TV documentary, the likes of Dame Joan Bakewell and Sir David Attenborough painted a portrait of Television Centre existing in a fug of cannabis smoke, while ex-Doctor Who and Blue Peter stars shed light on the enthusiastic appetite for “bonking” in dressing rooms.

“There was a lot of it about, no question,” says Ball, who was seen recalling how two Play School presenters had been stoned on screen – a revelation he now regrets (“I upset them, and I’m sorry I upset them, I didn’t mean to,” he says). As for the darker side of the Beeb unearthed in light of the revelations about Jimmy Savile: “I never saw any sexual harassment or anything like that,” he says. “Except we all knew – I knew in Manchester, before I was in television and before he was in television – that Jimmy Savile was dicey. He really was.”

In the 90s, Ball left the Corporation when resources started to be diverted from factual shows to dramas like Grange Hill and Byker Grove. “All of us – myself, Roy Castle, Tony Hart, Johnny Morris – we had to fight for our budgets. So I walked away. But as I walked away, because of the impact of the shows, the corporate world beat a path to my door.”

He did public outreach work for the likes of Rover and British Gas and National Grid, and also wrote and produced a series of educational stage musicals. “I’d wanted to write a musical since I was in the Forces,” he says. “So I had a ball. And, between you and I, it was a more lucrative career than television had ever been. We were working to three-and-a-half thousand kids a day. It was fabulous.”

In recent years, Ball has made headlines as an outspoken climate change sceptic. During our conversation, he insists he doesn’t want to get embroiled in it (“I don’t do climate change any more,” he tells me), and yet seems drawn to keep picking at the scab, because it’s a subject he’s clearly passionate about.

Surely the overwhelming consensus among the world’s climate experts can’t be wrong? I suggest. “Everything I said publicly on climate change in the late 1990s – every single thing – has been proven correct,” he insists, before reeling off a list of statistics about ice sheets, sea levels and cyclical weather variations. I ask if his work on behalf of car manufacturers and energy producers makes him partisan – a suggestion he finds “outrageous”, insisting they come to him because they trust his views, not because he’ll fit them to suit their agenda. “They wouldn’t ask me if I didn’t talk sense,” he says. “And by that I don’t mean talk their language, I mean talk sense.”

Something else he’s exercised about is the “frightening, terrible” shortage of students signing up for maths and sciences; he thinks combining physics, chemistry and biology into ‘triple science’ has been a disaster, resulting in “a watered down version of all three”.

How about his own children – did he succeed in instilling a rigorous scientific and mathematical understanding in them?

“I’ve always said you can’t teach your kids anything, but they copy everything you do, to a certain extent,” he says. That’s borne out by the fact one of his sons, Dan, is an engineer, the other, Nick, works in film, and daughter Zoë… well, you’ve probably heard which branch of the family trade she went into.

“I’m so proud of them all,” says Ball. “Zoë’s first career was as a ladette, if you like, which I think was a justified thing to be doing – asking: ‘why are the lads getting all the breaks? Why can’t we girls admit to being frivolous and silly and drinking a bit too much on occasion?’ And now she’s come back with a second career that’s bigger than the first, which was a similar case with me – I was 39 when I started Think of a Number.”

But is Zoë any good at maths? “No,” he says. “But she doesn’t need to be.”

When Zoë was presenting Live & Kicking on Saturday mornings, Ball was once brought on as a surprise for her birthday. “They put me in a big gorilla suit and sent me on to the set,” he recalls. “I went ‘Raaaar!’ and she just went, straight away, ‘It’s me dad’”.

In 2012, Ball, then 74, became the oldest ever contestant on Strictly Come Dancing – a fact his daughter, who presents spin-off show It Takes Two, only found out when it was publicly announced (Ball hadn’t told her because he wanted to avoid any suggestion of nepotism).

“My wife Di – who’s a dancer – and I were on holiday in Spain when I got the email asking me to do it,” he recalls. “The first thing we did was go to the bar and have a couple of large vodka and tonics. And we thought, well I’ve got to do it, haven’t I?”

Sadly, his Strictly experience was blighted by bad luck – not least losing his partner, Aliona Viali, to an ankle injury, leaving him just two-and-a-half days’ rehearsal with replacement Iveta Lukosiute – and he was the first to be voted off. “It was so sad to go out,” he says. “But I was chuffed to be the oldest contestant, really chuffed.”

Around 10 years ago, Ball was included in a Radio Times list of TV’s greatest eccentrics. Having worked with the likes of Magnus Pyke, David Bellamy and Professor Heinz Wolff, he doesn’t consider himself eccentric, particularly. “I tried to be funny, not eccentric,” he says. “But I’d like to be eccentric.”

Would he, perhaps, be happy accept the title of national treasure? “Willingly,” he smiles. “If it means something very old that’s just been dug up, then that’s probably me.”

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