THE leadership contest is settled, producing a winner with an enviable margin of around two to one. But that’s just the start of another race: three months until the Brexit deadline, and still only four possible outcomes: leaving with a deal, leaving without a deal, postponing yet again (for an election or a second referendum), or straight revocation.

Meanwhile, the party needs credible policies in the areas neglected during the Brexit debate – tax, health, welfare, education, environment, social care, policing. All this while – if one leaves aside the SNP for a moment – the polls have four UK parties closely grouped, none on more than 25 per cent of the vote.

Jo Swinson and the LibDems – who did you think I was talking about? – have at least the advantage of a clear Brexit policy: to scupper it. Ms Swinson, like everyone advocating a second referendum, assumes (a big assumption) that it would offer an option to overturn the first result, and that that option would win.

Still, the Liberal Democrats, like the Greens and the SNP, are internally united. Indeed, given that 48 per cent of the electorate voted Remain, it’s slightly mysterious that it took them so long to pick up those votes, though the European elections at last indicated a surge.

They have only 12 Westminster MPs (Stephen Lloyd left; Chuka Umunna joined), a low place on the starting grid. Still, the Brexit Party, with similar poll numbers, will probably, as Ukip did, find it harder to translate support into seats than the LibDems, who’ve always been doughty – many think dirty – election street-fighters. It seems quite likely, for example, that they’ll pick up Brecon and Radnorshire next week.

Another possibility is defections from other parties. The LibDems could double their parliamentary strength instantly if the non-aligned groups the Independents (where Heidi Allen now is) and the Independent Group for Change (led by Anna Soubry) followed Mr Umunna’s example – something as likely as not.

There are, too, quite a few Labour MPs who believe Jeremy Corbyn neither deserves, nor is likely, to gain power, while Sir Ed Davey, who lost to Ms Swinson, hinted a couple of weeks ago that half a dozen Tory MPs dead set against “no deal” might cross the floor to the LibDem benches. Cabinet resignations are mostly irrelevant, but defections are another matter.

They would simultaneously (by demolishing the minuscule majority and boosting LibDem numbers in the Commons) put us in General Election territory and Ms Swinson in a much stronger position. It’s possible to imagine a situation, perhaps within weeks, where the LibDems might be not far behind the Nationalists in Commons numbers.

While the LibDems won’t take seats from the SNP over Brexit alone, there’s no reason why they shouldn’t on other issues. If they pick up seats from Labour and the Tories in the rest of the UK – probably mainly in Remain areas, but also where the candidates are seen as hardline or unpopular for some other reason – it’s not at all difficult to imagine a scenario in which they exercise the balance of power and the ability to determine the nature of a future government.

It’s still hard to see them as the largest party, but if Ms Swinson plays a blinder and proves popular (as, though it may be hard to remember, “I agree with Nick” Clegg briefly was), if Mr Corbyn remains toxically unpopular, if the Tories lose a lot of seats to the Brexit Party, and lots of Remainers vote tactically, even that may not be a total fantasy. Ms Swinson should probably be heartened by the vigour of Labour attacks on her time in office.

Read more: Swinson: I will do whatever it takes to stop Brexit

Much depends not on the LibDems themselves, but on whether Boris Johnson can revive and hold together his party and deliver a Brexit Parliament can endorse, produce some plausible reason why not, or engineer some unforeseen electoral stroke of genius. None looks very likely, but that may be why the Tories endorsed him; even if it’s a reckless 100/1 gamble he can do it, it’s pretty well certain no one else could.

All the same, the LibDems have the same urgency when it comes to timing as the incoming Prime Minister. They need to muster their forces and strike before the end of October, because if the UK leaves, the principal reason for anti-Brexit voters to back Ms Swinson vanishes. “Stop Brexit” is not the same as “Let’s apply to rejoin the EU”.

That will be the case even without a deal; even if the consequences are terrible, they are unlikely to be as apocalyptic as Remainers, for obvious reasons, now paint them. The political narrative and policy objectives will shift to adapting to the new circumstances.

The imperative to get out in the next three months may be a sine qua non for saving the Tories’ electoral bacon; but there’s an equal urgency for the LibDems to stop it by then, because it’s now not just their primary objective, but their chief raison d’être. If the UK goes out, so does the main reason to vote LibDem.