Ukip, not Labour, are set to have a leadership crisis after the Stoke and Copeland by-elections

Strange to say, but by this time next week Labour could have lost one or even both the by-elections it is defending, and, while there'd be some understandable excitement and some long faces in the Labour Party, Jeremy Corbyn's grip on his party would only be a little less secure than it is now.

Mr Corbyn retains the loyalty of the grassroots, mostly has the unions behind him, and no credible candidate on the centre-right is in a position to unseat him. The “best” that might be imagined is that another, more effective, version of Mr Corbyn, such as shadow Chancellor John McDonnell or the thoroughly untested Rebecca Long-Bailey, now shadow Business Secretary, could pursue Corbynism through other means. The policies wouldn't change, the divisions over Europe, defence and the economy would remain, and the poll ratings would remain dismal. What's the point?

In that sense, what the voters of Stoke and Copeland do doesn't mean much for the principal opposition party. The Stoke result will, however, mean a great deal for Ukip. Rarely has a political party and its leader, in this case doubling up as its “local” candidate, fumbled such a golden opportunity to gain the political initiative. After all, Stoke is the Brexit capital of Britain, with the largest proportion of Leave voters in the referendum, plus the lowest turnout in the last general election, ample evidence of the disaffection Ukip thrives on. Yet Paul Nuttall’s campaign has stuttered badly, as he has run away from some, to put it kindly, galling errors of judgement, and it is not certain, by the looks of things, that he'll turn up for the declaration.

Indeed Ukip, rather than Labour, could easily be looking at yet another leadership crisis in the coming weeks. It takes a special talent to mess up as badly as Ukip have in Stoke.

The weakness of Labour and Ukip, with only the mildest revival in Liberal Democrat fortunes, leaves the Conservatives as the biggest beneficiary of current trends. Labour MPs pondering whether to quit and force more by-elections may start to think twice, given that unforeseen factors can conspire to strengthen Mr Corbyn's position.

Theresa May and her party enjoy commanding leads in the polls, with little sign that any of the three main opposition forces in England will put up much of a fight next time round. Even if the Tories don't win Copeland from Labour they should feel well satisfied with how party politics are going. Even the pesky SNP offers the Conservatives consolation that Labour weakness north of the border mean a Labour government in 2020 is virtually impossible.

The Tories must, though, fear what may soon engulf them and the nation: a sharp Brexit-driven economic slowdown with all that implies for unemployment, wage growth, the property market and living standards. The opposition is shambolic and divided but, given what's coming, the Tories would be foolish if they rely on that alone to keep them in power.