Boris Johnson has got the election he wanted – thanks to Jo Swinson

Jeremy Corbyn was forced to support an election by the Liberal Democrats and Scottish National Party

No sooner had I written about the election paradox – that, if it looks as if one side will win, the other side won’t vote for an election – than Jeremy Corbyn decided his side would vote for an election after all.

He probably believes that he will win, although those around him are likely to be less optimistic. At the last election, most of his inner team thought on election night that Theresa May was heading for a large majority. Nick Brown, Labour’s chief whip, is said to have argued against backing an election at shadow cabinet this morning.

But this is a tactic, not a real change in Labour’s view. The ground was cut from under Corbyn’s feet by Jo Swinson, the Liberal Democrat leader, and Ian Blackford, the Commons leader of the Scottish National Party. It became clear overnight that Boris Johnson had the votes he needed for a December election, so the shadow cabinet had to decide whether to accept it or to go to the polls having opposed the idea.

And the Lib Dems and SNP have reasons of their own for wanting an early election. Both parties stand to gain seats. The Lib Dems are at 18 per cent in national polls, twice the 8 per cent share they won last time. The latest poll in Scotland suggested the SNP would gain 13 seats to take 48.

They even have arguments of principle for backing an election. It may be that an election is the best hope of preventing Britain leaving the EU. Swinson and Blackford can point to the vote last week for the principle of the legislation to put Johnson’s Brexit deal into effect.

If you believe that bill is eventually going to go through – if, for example, the 31 January date turns out to be a hard, final deadline – then an election offers the better prospect of cancelling Brexit. If the Conservatives and DUP together lose just seven seats compared with 2017 (and assuming the Brexit Party doesn’t make up the losses), then there will be a majority for Labour’s plan to hold a second referendum.

But the hard truth is that this is an election that Labour MPs do not want. They have been betrayed by the SNP, in echoes of 1979, when an SNP motion of no confidence in James Callaghan’s government triggered its downfall seven months early. Many Labour MPs will refuse to vote for an election today, but Corbyn has already been on TV welcoming the challenge.

This election is what Boris Johnson wants. The Dominic Cummings faction in 10 Downing Street has won out, and the Cummingsesque side of the prime minister’s brain has prevailed. If Johnson had written two articles, in favour of and against an early election, he would have preferred the one in favour.

It would have set out the argument of his chief of staff that a December election is Johnson’s best chance to win a secure majority. He can fight it on a clear message of promising to deliver a Brexit that has been blocked and delayed by a naysaying parliament.

In the other article setting out the arguments for an election after Brexit, Johnson would have noted that the voters rarely reward politicians for delivering what they want. He probably would have quoted his hero Winston Churchill, thrown out by an ungrateful nation after winning the war.

Johnson starts this campaign in a commanding position, but he should worry about holding an election when it is not strictly necessary. He may be right that parliament, having voted for his Brexit deal in principle, would have dithered and delayed in practice. But he never tested MPs’ willingness to agree a more reasonable timetable for his bill. The voters did not like May holding an election when she did not need to. Will they be more forgiving of Johnson?