IT is a Friday afternoon on the Daily Telegraph comment desk, early June, 2012. The phone rings. I pick up. The ensuing conversation goes something like this. “Hello?” “Ah, yes. Yes. Um … hello … it’s …um … “ “Hi Boris, what’s up?” “It’s just … um … ah … about this Sunday … “ “What about it, Boris?” “Well, the thing is I … ah … might have to file my column a bit later than usual. You see, I’ll be … um … on a boat with the … um … well … the Queen.”

This was not welcome news. Boris Johnson warning he would be filing late was like Quentin Tarantino warning his next film would be violent. Boris always filed late (we kept a yellowing copy of a letter dispatched by an exasperated former editor many years before, warning that if he continued to so spectacularly miss deadline his column would simply go unpublished); if he felt the need to mention it in advance, something extra grisly was clearly looming. “Look, Boris, it sounds like you might be a bit busy. Shall I ask someone else to fill in this week?” “Gosh … no, no … I have a watertight plan. I think. Yes … I should be off the boat by around … ah … three-ish. I’ll get the piece done quickly after that.” “You’re absolutely sure?” “Quite sure. Well, probably. Yep … so … um … okay, bye.”

Sunday arrived and I watched the giant office TV screens as the Diamond Jubilee flotilla chugged down the Thames in the pouring rain: hundreds of boats, many bearing the great and, occasionally, the good, the glittering Royal Barge Gloriana, the Little Ships of Dunkirk, the Spirit of Chartwell with the Queen and the Duke of Edinburgh on board. No Boris, though. Then I saw him – the Mayor of London was with the Yorks and the Wessexes on the Havengore, the doughty little craft that carried the body of Winston Churchill along the same river during his state funeral. He’ll like that, I thought.

The hours passed. By three-ish, the Mayor of London remained afloat, waving a tiny tourist Union flag at the shore-side crowds. Four pm passed; five came and went. Boris was still on the boat. By 6pm, finding my eminent columnist’s mobile switched off, I was starting to panic at the prospect of a large white space on the next day’s comment pages. I called up a startled colleague and demanded 1,200 words on something – anything! – within the hour. Then, at 7.30pm, with all hope extinguished, my email inbox pinged. There was Boris’s column. It was a Johnsonian stream of consciousness about his day hobnobbing with the royals; it was untroubled by punctuation; it was, once we’d added some commas, full stops and paragraph breaks, magnificent. He had written it on his Blackberry, at the back of the Havengore.

That is Boris Johnson: frustrating; chaotic; selfish; perpetually on the verge of blowing it; lavishly gifted. It’s the Boris who could not stop himself publishing 4,200 words last Friday night in the Telegraph, setting out his vision for Brexit and the Britain beyond, knowing full well it would be seen as a blatant leadership bid. Ruth Davidson tweeted in response that, on the day of the latest London terror attack, politicians’ “only thoughts should be on service”. Amber Rudd, the Home Secretary, accused her Cabinet colleague of “backseat driving”. Michael Gove, the Foreign Secretary’s fellow arch-Brexiter, distanced himself from the suggestion Britain should no longer pay anything to the EU after leaving, even for access to the single market The reheated claim that Brexit could mean an additional £350 million a week for the NHS led to a stinging rebuke from a “surprised and disappointed” David Norgrove, head of the neutral UK Statistics Agency. Cripes.

There are, I think, three main qualities that should combine in the DNA of the political leader, all of which operate on a sliding scale: ambition, judgment and integrity. The first is a given – only those with the hungriest of eyes, those fiercely driven by the will to power, would seek out and endure the strains, punishments and high-wire glories of the highest office. The second should be a pre-requisite but isn’t always. The third is the one that I believe matters most: the one that marks out those who deserve to wear the crown from those who merely want to. Integrity is the habit of selflessness, the willingness to bear passing unpopularity in pursuit of what is right, the ability to resist the temptations of short-term political gain in favour of the long-term national interest. Done right, it licenses courage and confers honour. We could all compile our own list; it’s the kind of game that leads to heated pub debates.

Of recent prime ministers, I’d say Theresa May and Gordon Brown have qualities one and three and lack the second. But for Brexit, David Cameron would have had a claim on all three: as it is, he also falls down on judgment. I would rate Margaret Thatcher and Tony Blair, certainly at their height, as triple-medal winners, or as close as any flawed human is likely to get. Donald Trump is nothing but a bloated orange sack of ambition – which, leaving too much room for greed, corruption, vanity and national immiseration, should mean instant disqualification from leadership. Boris Johnson is in grave danger of ticking the same solitary box.

In the current choppy waters, when so much is fluid, when so many difficult and sometimes unknowable decisions must be made, and when the short and long-term often seem in direct competition, integrity and judgment are rocks we could reliably cling to. Mrs May is not the future; she is barely even the present. Perhaps, of the current Cabinet, Ms Rudd comes closest; though still relatively unknown, she seems most likely to hold together the internal Tory coalition and at this stage is supported, in private at least, by the most credible grandees. There is also a growing sense among the 2010 intake that, by 2019, when and if Brexit occurs, it will be time to fall in behind one of their own number and seek to return to more prosaic governing concerns.

But it won’t be the Foreign Secretary. He’s going down; his shipmates, even the rats, are deserting and no one fancies mounting a rescue mission. The good ship Boris Johnson is, it seems, finally about to slip beneath the waves.