At a time when running has never been more popular with generation Z, one man is proving that it is not just a young person’s game. The oldest athlete in this Sunday’s London Marathon is 88-year-old Harry Newton – whose remarkable running journey only started by chance when he was 57.

Since then Newton, a retired grocer from Macclesfield, has completed 31 marathons, including 21 at London and another by jogging 461 times around his garden during lockdown. And he has a simple message for nervous first timers this weekend. “Don’t try to run too quickly, and keep a steady pace,” he says. “And make sure your bowels are empty.”

As Newton speaks his wife, Phyllis, who is a sprightly 85, laughs in amusement. What does she make of his unlikely journey? “She always tells me I’m daft, and she wishes I wasn’t doing it, but she’s been a terrific supporter,” he says. “She will be there this year, along with around 20 members of my family. And this year I will be in the VIP area – I get to choose when I start and there are private toilets as well!”

Newton’s late-blooming started by chance when he attended a meeting of the Northern Council of Grocers in the Lake District. “There was a chap from Mars confectionery who spoke to us about the London Marathon,” he says. “He said if anybody would like to raise some funds for the Grocers’ charity, I might be able to get you an entry form.”

A few days later a form arrived in the post and, after getting the nod, Newton laced up a pair of running shoes for the first time in the autumn of 1994. “When you’re on the farm, you tend to live the life of a farmer,” he says. “And similarly as a grocer, you also work long hours. So I wasn’t a runner at all before that.”

Training, it is fair to say, didn’t go quite to plan. The longest run Newton did before his first marathon was just nine miles because he had knee issues. And when he got an X-ray a week beforehand, his doctor delivered a blunt message.

“He said to me ‘although it’s not unusual for a man of your age, there is some wear and tear in that knee, and I do not see it standing up to any marathon’,” he says. “But I had a couple of thousands of pounds sponsorship riding on it, so I thought I would give it a go.

“That first one was slow, but I got round in five hours and 10 minutes by running and walking,” he adds. “Although I hurt all over for about a month afterwards.”

By then the marathon bug had hit and it never let go – including running one in his back garden. “That was when we weren’t allowed to go out much,” he says. “So I thought the answer was to run around the garden. I strode it out to about 110 yards. And I just kept going round in circles until my watch told me I’d done enough. I think it was 461 times.”

Newton’s personal best at London is three hours, 52 minutes and 30 seconds – set when he was 70 years old. He will be slower this year, but last September ran Morecambe in five hours and 56 minutes, well inside the six hours and 10 minutes limit to get a Good For Age place for over 85s.

Like any runner he is determined to give it his very best on Sunday and will take to the start line wearing a pair of Saucony super shoes, which normally retail for £280.

“There was a sale in a local shop in Wilmslow a month or two ago. So I grabbed a pair.”

The world championship bronze medallist Julia Paternain, who is also racing in the same shoes on Sunday, says she is amazed by Newton’s achievements. “The fact that he’s running a marathon at 88 is just so inspiring,” she says. “And it’s really cool that I’ll be in the same company as him.”

And whatever happens, Newton isn’t finished yet. “A few years ago, I probably wouldn’t have thought to still be running at 88, but I’ll keep doing it as long as I feel as if I can,” he says. “I will be slower every year, won’t it? But that’s age. And you can’t do a lot about that.”

Before he goes, he has a final nugget for those of a certain age who are inspired to follow in his footsteps: see a physio and get strengthening exercises to stay injury-free – and don’t be afraid to give it a go.

“I’ve found that very helpful,” he says. “And for the last five or six years, touch wood, I have been pretty clear. Sometimes you do go out and you think, ‘Oh, this knee’s pinging a bit this morning’, but you run a mile or so and you forget all about it, don’t you?”