Forget the cigar, the homburg and the V-for-victory sign. If Winston Churchill were around today, he’d be pounding the streets in T-shirt, shorts and chunky trainers. Jogging is an almost compulsory obsession for any Tory alpha male. Boris Johnson and Jeremy Hunt are forever out running; Michael Gove has lost a drastic amount of weight racing around west London; and Boris has revealed he’s down to 15 and a half stone, from 16 and a half.

He’s also declared he’d freeze obesity taxes on fattening food — the answer to losing weight was more exercise, he said — and admitted to failing to keep up a vegan diet (he likes cheese too much). But he is certainly looking slimmer since he started going out with Carrie Symonds, 24 years his junior. If he can’t shrink the age gap, he can shrink the weight gap. When he was foreign secretary, he used to go jogging with his security team. ‘We used to get up at six o’clock every morning wherever we were and do a very, very lackadaisical run around whatever national landmark — Red Square, Sydney Harbour,’ he explained, in a recent Spectator interview.

The jogging craze began with the previous Conservative administration. Both David Cameron and George Osborne graduated from biking to work (before they rose to power) to jogging around the streets of Westminster once they were in office. It’s largely a male thing, and a generational thing too. Theresa May (born 1956) wouldn’t be seen dead in a singlet. And can you imagine Margaret Thatcher (born 1925) in a pair of trainers? The new generation of jogging Tories were born within a seven-year period: Boris Johnson (1964), Jeremy Hunt (1966), David Cameron (1966), Michael Gove (1967) and George Osborne (1971). They were children when the American inventor of jogging, Jim Fixx, wrote his 1977 bestseller, The Complete Book of Running. Forty years later, when they entered middle age and faced the dreaded tummy and horrifying moobs, jogging had become mainstream.

In the old days, it didn’t matter if a Tory politician was fat — look at Churchill and Ted Heath. It was almost impossible not to be fat. Think of the endless receptions, speaking engagements, three-course constituency dinners and late-night parliamentary sittings lubricated with gallons of Château Paintstrippeur in the many Commons bars. Now even Nicholas Soames has slimmed down (not forgetting the King of the Tory Slimmers, Nigel Lawson — though he wouldn’t have gone jogging in a million years).

But it isn’t just middle-aged politicians who are losing weight; it’s middle-aged professional men generally. Upper-middle-class chaps — who would once have rejoiced in red faces, big tums and red cords — are now whippet-thin. Their favoured party outfit — jacket plus T-shirt with lightweight trainers — only really looks good if you’re thin.

The elderly whippet look is catching on everywhere. I have been bicycling along the Outer Circle of Regent’s Park for more than 30 years. For the first 20, I was one of very few cyclists, often overtaking Alan Bennett travelling at a stately pace on his vintage boneshaker. These days, I’m the slowcoach, overtaken by high-speed pelotons of skeletal bankers and lawyers, wrapped in lurid Lycra stamped with Tour de France sponsors’ motifs.

Snapping at the heels of the competitive middle-aged professionals are the millennials — who drink much less, eat more healthily and take more exercise than the generation above them. And then, at the other end of the age spectrum, there’s the dreaded spectre of death and — worse for many middle-aged men — retirement.

So how do you keep up with the younger generation and fight off the Grim Reaper? Get thinner. Just ask Osborne (on the 5:2 diet) and newscaster Huw Edwards, who has shed three stone thanks to boxing and a thing called TRX (Total Resistance Exercises, a system developed by a US Navy Seal, where you suspend your body from a tree with a vast elastic band).

It’s all rather undignified and vain. How much better to grow old gracefully, like Kenneth Clarke, the heroic panatella puffer and beer drinker, who at 79 has announced he will stand down at the next election. We shall not see his like — or his waistline — again in future great Tory politicians.