Just how wild and mercurial could this election prove to be?

Well, one instructive place to start is with a pub quiz question: who was the last British prime minister to lose his seat? The answer is the Tory Arthur Balfour, who had in fact already resigned just before being crushed in the great Liberal landslide of 1906. While there might be bonus round points for knowing the same fate befell the right-wing Australian premier, John Howard, in 2007, there are none to be had on our own side of the world, where nothing similar has happened in the 113 years since Balfour’s battering at the ballot box.

Why is this relevant? Well, if you speak to Labour’s excitable activists, they think they’ve got a real shot at political decapitation. (And yes, I know in these times the wise counsel is to go easy on violent imagery, but seeing as Boris Johnson has personally argued that a stop-and-think approach in choosing words is to “impoverish” the language, I’m certain he wouldn’t want us to go PC on his account).

Are these activists deluded? Given the opposition’s grim starting point in the opinion polls—averaging just 25 per cent in the latest surveys—you might very well think so. Uxbridge and South Ruislip (and plain Uxbridge before it) has been solidly Conservative for two generations, even returning a Tory with a solid majority in a by-election during Tony Blair’s first heady summer, when Labour was running at well over 50 per cent. Moreover, as psephologist Lewis Baston tells me, prime ministers and other leaders can ordinarily expect a bit of a personal boost.

And yet reports from political cabinet suggest that the prime minister himself flagged CCHQ analysis ranking his seat as being at risk. The case for an upset that would entirely eclipse the “Portillo moment” of 1997 in the collective memory starts with the relatively close result last time. In 2017, Johnson secured a narrow overall majority of the ballot (51 per cent) but a strong Labour showing reduced his lead to 5,000 votes, small enough for it to just about rank as marginal and smaller than any other prime minister’s majority in modern times. The seat is on the edges of London, and the nostalgic and nationalist recent turn of the Tories was never designed for a diverse capital city that has lurched a long way left during the last decade.

Put all this together, and you explain the buzz around the campaign of the 25-year-old local activist, Ali Milani, whom Labour have tasked with trying to unseat the PM. You explain, too, the many excited rumours on the Labour side that Johnson will soon embark on “the chicken run” to find a safer seat. Some thought he looked embarrassed at the dispatch box when taunted about the possibility in recent days, but when I saw Jeremy Corbyn raise the possibility of a relocation in the Commons yesterday, I thought Johnson looked pretty relaxed as he yelled back from his seat “come to Uxbridge, you’re welcome.”

And—for once—I’m inclined to believe his people in No 10 when, adopting their master’s voice, they describe the suggestion of Johnson upping sticks as “tosh.” I say that, first of all, because it would at a stroke destroy the Boris pose as a man of derring-do, the soul of boundless optimism who got a Brexit deal when everyone said it couldn’t be done. If the public were now to see him scarper away from the first flash of potential trouble, that would be scotched even more rapidly than Theresa May’s fabled steadfastness two years ago, when she began ditching parts of her own manifesto while insisting that nothing had changed.

But secondly, beyond the potential unravelling of the Johnson story, there is the question of the numbers. British politics has splintered with remarkable speed in the 30-odd months since May and Corbyn split over 80 per cent of the ballot. One mark of that is the likely collapse in the number of MPs with an absolute majority: of the 304 Conservatives elected in England and Wales last time, Baston suggests, some 242, like Johnson, enjoyed 50-plus per cent. A new mega-poll of 46,000 people, conducted for MRP by the campaign Best for Britain as it launches an appeal for anti-Brexit tactical voting today, suggests that this may now have declined to just a single Conservative MP.

But if Johnson looks extremely unlikely to hang on to his thin overall majority, his majority over his opponents could actually grow. Why? Because the anti-Conservative vote is splintering even more than that of the Tories. At least part of the great swing from Labour to the Liberal Democrats in the European election looks likely to be sustained into this general election. Indeed, Best for Britain indicated that their detailed polling suggests that in Uxbridge—where the Lib Dems notched up a derisory, deposit-surrendering 4 per cent last time—it is now Jo Swinson’s party which poses Johnson the greatest threat. I find that hard to believe, especially because tactical voters will look at last time’s results and deduce it’s only Labour that has any shout.

Nonetheless, the fact there can be any argument at all about what the “tactical” anti-Johnson vote is in Uxbridge shows how difficult he will be to dislodge. Even voters with a single-minded urge to show him the door may end up cancelling each other out, by swapping from (say) Labour to the Lib Dems while others go in the opposite direction.

And if a splintering anti-Johnson vote is likely to save the prime minister in his own seat, it could also work magic for him nationwide. The media is likely to concentrate on a small number of Remain constituencies where the Lib Dems look likely to dislodge the Tories: you may have already read about Cheltenham and St Albans, and if not, you will soon. There will be less attention, though, on the myriad seats across the country—both Remain and Leave—where the splintering of Remain votes between Labour, Lib Dem and perhaps Green, SNP, and Plaid will be sufficient to let a relatively cohesive Leave bloc backing the Tories take the win.

Can anything alter that? Well there is one thing that might do so, and is easier to imagine than close co-operation between Labour and Lib Dem parties whose relations are more bitter than ever. Namely, a new splintering of the Leave vote, through a resurgent Brexit Party. I don’t know if Nigel Farage, who has been pretty quiet of late, is holding out in the hope of a re-elected Johnson appointing him ambassador to Washington, or whether instead he is biding his time to go on the offensive against him after tomorrow’s “do or die” Brexit deadline is missed. But I do know that if it is the latter, Johnson really could be in trouble, including in Uxbridge where Ukip marginally exceeded its dismal nationwide score last time around.

Britain’s bizarre recent politics now confronts an additional paradox. Those who want to thwart Johnson and the hard Brexit he promises must now vest their hopes in none other than Farage.

*This piece has been amended to delete an erroneous citation of estimates of the 2016 Leave/Remain split in the prime minister’s seat