In pictures: Is Boris Johnson ready for accelerated ageing? How being Prime Minister visibly takes its toll on those in the role

Oddly, one of the first things every new Prime Minister considers is their legacy.

What will they leave behind? What will the lasting memories of their time as “first among equals” be?

To be brutally frank, the standard answer is “not much”.

However, if some predictions about Boris Johnson’s time in No 10 prove correct, his legacy could be profound and long-lasting.

And not in a good way.

The man many – several of his Tory Party colleagues included – consider to be fundamentally unfit for office could, according to some, prove to be the last Prime Minister of this United Kingdom.

They think Scotland, Wales and Northern Ireland might see the ascension of the new man at the helm of the highest office in the land as the last straw.

And that, in turn, could lead to the good ol’ Blighty he claims to love so much becoming four separate countries, including a united Ireland.

Worryingly, it is not the usual collection of crackpots predicting this – and Nicola Sturgeon must think all her Christmases have come early.

Greater political thinkers than I – I know, hard to imagine – say we were set upon the path to this fine mess by Mrs Thatcher, who moved away from the collective style of politics embraced in the aftermath of the Second World War to a more individual-based ideology.

Less “all for one”, more “what’s in it for me?”.

This was weaponised by David Cameron’s catastrophic unleashing of the Tory Party civil war over Europe on the country as a whole.

It’s not going to be an easy ride for the new PM, though and that leads us to the only part of his possible legacy that is an absolute certainty – he’s going to age dramatically before our very eyes.

Just look at his immediate predecessor in Downing Street.

Theresa May faced hecklers in the streets, trolls on social media, desperate division in the Commons and open warfare in her Cabinet over Brexit during her undeniably tough stint as PM.

© Chris Radburn/Stefan Rousseau/PA Wire

If you compare “before” and “after” shots of every recent PM, the strains of the job are clear to see on their faces, few more so than Mrs May.

In her three and a bit years in power – and I use the term loosely – you could argue that she’s had one of the roughest rides since Neville Chamberlain copped all that flak over his mishandling of that Hitler fellow.

The so-called “Maybot” never exactly exuded joie de vivre but recent pictures show a broken woman at the end of a long and punishing road.

Remember her speech at 2017’s Conservative conference, a dreadful cough, falling letters and a Boris-themed prankster?

Some saw that as the symbolic moment of her premiership but I suppose you have to hand it to her for somehow sticking around until now.

David Cameron was PM for just over six years and when he was elected at the age of 43, he was a toddler in Prime Ministerial terms.

Shades of Tony Blair surrounded the fresh-faced Conservative, whose youth and energy had supposedly reinvigorated a Tory party not generally known for either.

Come 2016, he was still in his 40s but looked really, really tired and that cherubic glow – remember the election poster that was basically just a close-up of his big, shiny face? – was gone.

It could have been so much worse for Cameron if he’d actually had an appetite for hard work.

Reportedly lazy, he moaned “Why should I do all the hard stuff for someone else, just to hand it over to them on a plate?” after delivering his resignation a few hours after Britain voted to leave Europe.

What a difference nearly three years made for Gordon Brown, though.

It rarely felt like the premiership was going to be particularly kind to Brown and after the credit crunch and 2010’s inglorious election defeat, his resignation must on some level have been a relief.

Sleep-deprived, sallow-faced and self-evidently miserable, the burdens of office etched themselves on to the former chancellor’s face.

© Dinendra Haria/Anadolu Agency via Getty Images

Sid James once said Tony Hancock told him his face had more canals than Venice and the same could be said for Brown who, having waited years for Tony Blair to budge, probably found being PM was not everything he had dreamed of.

Speaking of Blair, if a week is a long time in politics, a decade in No 10 must be a lifetime, but even so his changing coupon makes for grim viewing.

When a charismatic, fresh-faced Tony ascended to the throne with a landslide general election victory in 1997, it felt as though politics was set to become a young man’s game after decades of being ruled by old codgers.

But as the Iraq War turned ever more disastrous, the years began to pile on. Ever-present eye-bags, pallid skin and a permanently furrowed brow all bore testament to the stressful reality of life in Downing Street.

John Major, PM for six and a half years, was already rocking the grey look when he took over in 1990 so his tenure looks more like a simple case of accelerated ageing.

In other words, an old-looking 47-year-old (heavens, that’s younger than me, I thought he was ancient at the time) became a very old-looking 54-year-old as Major was harried and harassed by factions in his own party.

Perhaps the strangest thing is that today, more than two decades later, he still looks pretty much the same – it’s as if leaving office has halted the ageing process.

His long-serving predecessor, Mrs T, was famous for sleeping only four hours a night and it seems that the Iron Lady’s lifestyle lent itself unusually well to the rigours of three-and-a-half terms as PM. Her notoriously steely disposition meant she rarely cracked in front of the cameras and she exited 10 Downing Street looking a little older but still pretty intact.

I’ll wager a large wedge the same will not be said about Boris Johnson.

But now he is actually Prime Minister, what happens next?

The honest answer is probably “not much” as Parliament broke up for its summer recess the day after he became PM and is not due back until September 3.

And we thought teachers got good summer holidays?

In his victory speech he pledged to deliver Brexit, unite the country and defeat Jeremy Corbyn. Well, let’s look at keeping those promises which, let’s be honest, isn’t a Johnson strong suit.

His “do or die” pledge to leave the EU on October 31 with or without a deal was dealt a blow before he even made it, with several MPs including Tories saying they would prevent him suspending Parliament in order to railroad the country into leaving.

And the EU has stuck steadfastly to its guns throughout this whole, sorry saga.

As for uniting the country, as already mentioned, many eminent pundits think precisely the opposite might come to pass, which is ironic for the leader of what’s officially called the Conservative and Unionist Party.

That just leaves defeating Corbyn which, let’s face it, is something the Labour leader is already doing a dashed fine job of doing himself.

The Tories’ majority is now just a couple of MPs so, if Johnson does not keep everyone happy – and that’s another thing he’s not proven good at – a general election could well be on the cards.

Johnson has repeatedly said in the past his political hero is Larry Vaughn, the obdurate mayor of Amity in Jaws. Johnson is not a details man and Mayor Vaughn chose to ignore one major detail – a huge great white shark was eating his constituents.

Johnson says he admires Vaughn because “he kept the beaches open” and it seems to me that in this scenario Boris will keep the beaches open no matter how many of us end up as fish food.