Jeremy Corbyn is well on his way to winning the next election – here’s how

As long as we stay in the European Union, which I think we are likely to do for the foreseeable future, the Conservative Party is unlikely to win an election. In which case, Jeremy Corbyn is likely to be prime minister. I have rehearsed the reasons for the first two steps of this argument before, but the third needs to be tested. This week we had a live test, in the form of the Peterborough by-election.

The Conservative candidate did badly, losing more than half of the party’s share of the vote at the general election, when the seat was closely fought against Labour. Nigel Farage’s Brexit Party did well, reflecting the failure of the government to take Britain out of the EU. And the Labour Party did badly, but not as badly as the Tories, and just enough to hold the seat.

That could be the next general election in microcosm. As long as Brexit remains undelivered, the Brexit Party will steal most of the Tory party’s votes. But the residual loyalty of the core Tory vote, and the single-issue obsession of the Farageists, will prevent the Brexit Party from wholly replacing the Conservatives.

That means the Leave vote will be split, making it hard for either party to win seats under the first-past-the-post system. The Remain vote will be split, too, but Labour will be able to defend its territory better than the Conservatives can defend theirs.

The Peterborough result is a better guide to how this might work than the European elections three weeks earlier. In the European elections, the Liberal Democrats overtook Labour to become the main voice of anti-Brexit protest.

But in Peterborough the Lib Dems were in fourth place. They won 12 per cent of the vote, which was more than the 3 per cent they won in the general election, after years of being squeezed in a Labour-Tory marginal. But they didn’t take enough Remain votes from Labour to deny them the seat.

This is not just a question of the difference between first past the post and the proportional system used for the European elections. The European elections were also seen by voters as a chance, above all, to express their views on Brexit, for and against.

In the Peterborough by-election, as in a general election, there are other issues – the NHS, schools, housing and crime. On those questions, Labour tend to do better than the Lib Dems.

Corbyn’s critics said his policy of facing both ways on Brexit was a disaster, and so it is, but it is not disastrous enough to stop him winning. Who knows what the party’s policy on Brexit would be in a general election? If this parliament ran on until 2022, it is quite possible that it would involve renegotiating the Brexit deal and putting the result to a referendum.

The failure to deliver Brexit means all previous assumptions about politics have to be revised. We may have passed Peak Corbyn, in the sense that the high excitement of the mass membership for what they see as true socialism has faded. It may be that the surprise popularity of Labour’s 2017 manifesto cannot be repeated. But the Peterborough result shows how Corbyn can go backwards and still win. Depending on how the votes split between the four, five or six parties, he may not even need the SNP to help him form a government.

What could go wrong with this prediction? There are two possibilities I can see, and probably many more that I can’t. The first is that Boris Johnson, or whoever is the new prime minister, could call an early election to try to secure a mandate for a no-deal exit. That might win back many of the Brexit Party voters, but it would be a risk and it would split the Tory party.

The second is that Emmanuel Macron or another EU leader refuses to agree to a further extension to the Brexit timetable in October. Then parliament would, I think, approve the withdrawal agreement rather than face a no-deal exit or revoke Article 50. But it seems unlikely that any EU leader would break ranks to try to force us out, because the European Union would not want to take the risk of a no-deal Brexit for which it would be blamed.

That is why I think the new prime minister will enrage all Leave voters, and the party that has just chosen him or her, by asking for a further extension in October. And that means, in 2022 if not before, a Labour government.