David Cameron today tells the Sunday Times that he will stay on as Prime Minister if Britain votes to leave the EU. He could scarcely say anything else, but he is clearly dissembling. A Leave vote would mean that he himself has to leave. This presents pro-Brexit Conservatives with a stark choice. Back Remain, and you betray your conscience. Back Leave, and you oppose your leader – and, furthermore, condemn him to resignation if Britain votes to leave the EU. In these circumstances, you will have helped to bring down the Party’s most successful election winner in modern times save only Margaret Thatcher.

This is precisely the conundrum that Michael Gove has been wrestling with. The Justice Secretary is insistent that it is his experience as a Minister that has tilted him decisively against Britain’s EU membership, but it has been clear for several years that he has become convinced that we should leave. Boris Johnson, however, is not a natural Brexiteer. The son of a former MEP who backs EU membership, the brother of an MP who takes the same view, and raised himself partly in Brussels, Boris has never been comfortable with Brexit.

For all his EU-bashing Daily Telegraph columns and stories – his “Delors plan to rule Europe” splash played a part in the 1992 Danish referendum that rocked the Maastricht Treaty – and the distinctly Eurosceptic report that he commissioned as Mayor, he has never said that we would be Better Off Out. Indeed, he recently told Bernard Jenkin that he has “never been an Outer”. The latter added: “Boris was quite open and frank about it – it was no secret conversation. He is genuinely torn but I hope he will change his mind because he is one of the few who understands that if we stay in Britain will be in a weaker position than ever before.”

And now, we are told, he has indeed changed his mind. Robert Peston, ITN’s Political Editor, tweeted yesterday evening that the Mayor will declare this evening that he will vote and campaign for Leave. It could be that the report will turn out to be misplaced: the Sunday Times reports him saying that “I’m veering all over the place like a shopping trolley”, and one can never quite tell what Boris will do. But the placing and timing of the story could make sense. Peston is one of Britain’s great official journalists, whose ceremonial place in breaking a political story is not unlike that of the Gold Stick in Waiting or the Clarenceux King of Arms at the state opening of Parliament.

Events would unfold as follows: Peston blows the starting trumpet, Cameron’s Marr interview this morning is upstaged, reporters scurry off to Islington, commentators jostle and thrash like feeding frenzy-crazed carp, the cameras plonk themselves outside the Great Man’s house, Marina is mobbed nipping out to Waitrose, the sense of expectation builds…and, as the sun sinks red into a bloody sky, the final dramatic stroke is struck. The Great Man’s Monday Telegraph column declaring for Out thunders off the printing presses, and he himself shuffles from his home, eyeballs gently rotating, in a state of artfully manufactured disarray. Er…umm….arrrggghh…yaaaaah!

But if such story management makes sense, such a decision would be harder to conjure. It is true that the Mayor’s behaviour during the run-up to the summit – the impossibilist demands for the primacy of British law within the EU, the hints and murmurs, the preposterous public visit to poor old Cameron in Downing Street – only make sense if he is already set on Brexit. None the less, to come out for it would pulverise the sedulous, creeping, nail-chewing advance that he has steadily made on the Conservative leadership for the best part of 15 years. The safer course by far would be to tuck himself quietly in behind the Remain campaign and wait for the shine to come off George Osborne.

Boris has crawled towards Downing Street with the caution of a slobbery-mouthed lion stalking a shimmer-flanked young gazelle. For him to leap lumberingly at his prey with a roar would risk it galloping off shrieking into the bush. Then again, the Mayor has never been the man for the safer course. It is true that he is now damned if he does and damned if he doesn’t. We return to the problem of him never having been for Brexit. If he goes with his history, he will look as though he’s backing down after a week of winding up: willing to wound, afraid to strike. But he veers off in a new direction, it will be towards open war – not only with his past, but with his leader.

The Mayor is sometimes mocked for having no convictions whatsoever. Certainly, his recent tergiversations will have done him no good with his Commons colleagues, who have always been cooler about him than the voters. Leavers will never be convinced that he is truly One of Them (that’s to say, One of Us). But I think that this view is wide of the mark. The best comparison is perhaps with another Tory Blonde Bombshell who parted with his leader: Michael Heseltine. The latter’s falling out with Margaret Thatcher was fired by a mix, impossible to separate, of frustrated desire and irrepressible conviction.

His resignation is sometimes said to have been about a trifle: a mere helicopter company. And so in a sense it was. However, behind it was something bigger. At the heart of the clash between the then Defence Secretary and Downing Street over who would take over Westland – Sikorsky or a European consortium – was a difference over the destiny of a nation. Where does Britain’s future lie? With our continental neighbours, or in the wider world? What is our place in the world? Here we are again. But this time the roles are reversed and the stakes are higher. This referendum fills the sky where one had to squint to see Westland – outside the Westminster Village, at any rate.

Yes, Cameron v Boris would have even more baleful implications than Thatcher v Heseltine. That conflict helped eventually to depose a three times election winner, undefeated at the polls, and pave the way for three terms of Conservative opposition – the longest period of Tory humiliation in modern times. This time round, the European question looms larger than ever, the referendum dramatises division, UKIP is with us and politics itself is more fragile. To date post-election, the Party has managed its differences extraordinarily deftly. But an Out decision by Boris might put all that to the sword.

Cameron and George Osborne, especially, have had their fallings-out with Boris, but this gang of three, and Michael Gove too, are not unlike – all roughly of the same age, all journalists or former SpAds, all at home in liberal London. They are part of a generation. Now there may be fratricide among the band of brothers. Perhaps Gove has titled Boris over the edge. Perhaps he will back off after all. Who knows what cocktail of ambition and belief is fizzing uncontrollably up within the Mayor? Maybe he thinks that only an Outer can next lead the Tories, or perhaps events are simply creating their own momentum. They all go mad in the end, the political legend runs. I can’t help wondering if the long wait and tension is driving Boris slightly bonkers.