With his shock of white hair, love of ancient Greek and tendency towards tangential speech, Stanley Johnson is very much his son’s father.

Never one to answer a straight question with a straight answer, our Skype interview to mark the globetrotting environmentalist’s 80th birthday last month is characterised by the sort of subtle obfuscation for which his eldest child, the Prime Minister, is notorious.

Describing the recent heatwave as "superbly awful", he soon reveals that he has returned from the second of two holidays since the coronavirus outbreak. The first – a trip to Greece in June when his son’s Government was still advising against all but essential travel – landed him in hot water.

"I only went for three days," he insists, although at the time he admitted he was spending a week at his villa in Pelion overlooking the Aegean Sea in order to "Covid-proof" it ahead of the holiday rental season.

"I could have said, ‘Look I’m going to be totally incognito’, but there would still have been someone who said, ‘There you are’. And then someone would say, ‘Boris’s Dad sneaks into Greece’."

In vintage Stanley style, he only attracted attention after posting a selfie of his masked arrival at Athens airport on social media, leading to an outcry from critics likening his behaviour to that of Dominic Cummings. "You’re not going to start talking about Barnard Castle are you?" he implores as I attempt to find out whether he received any fallout from Number 10. Carefully swerving the question, he insists that he absolutely "isn’t going down that route".

UK Prime Minister Boris Johnson’s father Stanley is hoping UK rejoins EU... for the sake of the environment

Despite the somewhat oxymoronic nature of clocking up the air miles while making the case for protecting wildlife, it seems the I’m a Celebrity star’s travelling days may be numbered.

Having been forced to postpone a third climb up Kilimanjaro because of the coronavirus, his main priority now is catching up on writing and reading. He has just finished the first of Maya Angelou’s seven autobiographies and is learning modern Greek.

He is also reading Around the World in Eighty Days – in French – as well as the proofs for The Warming, the second novel in his latest "thrillogy" set to be released for Christmas.

The former MEP, who has written no fewer than 26 books, including a two-volume autobiography, adds: "You suddenly realise that there are an awful lot of things you haven’t done.

"Not as far as travelling and adventure is concerned, I think I’ve pretty much done the whole world.

"I still feel full of vigour and energy and enterprise, but I think a more reflective moment is called for, actually." Recalling how, on the morning of his 40th birthday, he nearly killed himself with a chainsaw, sawing a tree branch on his farm in Exmoor, Johnson certainly has a keen sense of his own impermanence.

"Mortality is just something we’ve got to live with," he chuckles. "What a disaster it would be if people didn’t die."

Referring to the six books he has written on world population, he adds: "I think that the idea that one should be transfixed by longevity, that is just nonsense. I mean, I would have been perfectly happy by three score years and 10. I’m already in a plus situation because I’ve had three score years and 20." Then comes the first mention of Boris, for making "an extremely good argument in The Telegraph in 2007" saying "if there’s one important issue in the world today, it is the issue of population growth linked with female education".

But can either of the Johnsons credibly make the case against overpopulation when they have each fathered six children?

"It’s a perfectly fair point," Stanley concedes.

I wonder what the patriarch of Britain’s leading family of overachievers actually makes of his offsprings’ accomplishments. While his eldest with his first wife Charlotte Fawcett, to whom he was married from 1963 to 1979, is in Downing Street aged 56, his daughter Rachel, 54, is a journalist, and sons Leo, 53, and Jo, 48, have City and politics careers respectively. Like all their half-siblings, his two children Julia, 38, an author, and businessman Max, 34, with his second wife Jennifer Kidd, also won places at Oxford, although Stanley – who himself read classics at Exeter College – .

"One person’s high achievement is another person’s average performance," he says.

"The family background which my wives have provided has been vital and then I would never, ever, underestimate the importance of schooling."

Seemingly desperate to change the subject, he adds: "Of course, I’m absolutely delighted that they are all making their way." He later texts me to reiterate how "tremendously proud" he is of all his children.

Counting milestones

So what are Stanley’s proudest achievements? Without hesitation, he cites winning the Newdigate Prize for poetry in 1962 as a real highlight – not least as he wrote the 98 lines of Chaucerian rhyme royal "between breakfast and lunch" when 21.

While other career apogees include the World Wildlife Fund’s Leader for a Living Planet Award and the RSPB Medal, his chief regret also dates back to his Oxford days – when he missed out on a "rugger blue".

"I see life as a game of rugger, really," he muses. "My tactic when I was playing was to catch the ball and bash forward. Sometimes you get the ball over the line but at any rate you instantly gain ground from kick-off."

Without hesitation, Stanley cites winning the Newdigate Prize for poetry in 1962 as a real highlight

With the image of his son taking out a schoolboy in a rugby game during a 2015 visit to Japan, I proffer the suggestion that bulldozing over obstacles may lack a little panache.

"At this crucial age of 80, maybe you have to put the bulldozer to one side and say, other people can do the bulldozing," he admits – although statements linking the coronavirus to intensive farming and insisting we need a carbon tax suggest otherwise.

Even on Brexit, the passionate Remainer cannot resist making the suggestion that the UK rejoins the European Environment Agency. "I’m talking about all the environmental legislation, the animal welfare legislation, the food safety legislation. We must be very careful we don’t throw that away, thinking mistakenly that we can get a free-trade agreement, without bothering about this great area of concern," he says.

Insisting that we should use the current situation to move in a "different direction", he adds: "I think the mistake politicians have made and continue to make is to bang on about the need for economic growth. Of course economic growth is vital, but what matters is the kind of economic growth we are going to get. You hope we’re going to emerge from this current crisis with a new perspective."

And how will Stanley Johnson emerge? "I’d like to think that people are coming to realise what I’ve been saying since 1973 – that nature is fundamental to economic growth."

He pauses and comes up with something that couldn’t sound more Johnsonian if it were wearing a blond wig. "We need to build back better," he declares. It seems that he may not have stopped digging holes, after all.

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