The prime minister is boiling the Brexiteer frogs: the water is getting hotter and none of them has jumped out of the pan

The frog-boiling is going well. Theresa May has turned up the temperature another notch and Boris Johnson has still not jumped out of the pan. Nor has Liam Fox, Michael Gove or David Davis.

At the meeting of the Brexit committee of cabinet on Tuesday, the prime minister came up with a plan so cunning no one could work out what it meant. She asked them to agree what would happen if there was no agreement about trade by the end of the transition period after Brexit.

The foreign secretary grumbled a bit, but agreed with the prime minister that the UK would then continue to apply the EU’s common external tariff until a new arrangement was ready. Considering that the systems to do anything else could not be in place by December 2020, the end of the 21-month transition period after leaving the EU, this did not appear to be a significant moment.

She might as well have looked around the committee members and said, “So that’s agreed: two plus two equals four?” Given the hard Brexiteers’ tendency to resist reality, however, she knew there was a slight chance Johnson would gather his papers and leave, saying he could not accept such Remoaner arithmetic.

British politics is in one of its strange phases when it is significant that cabinet ministers accept reality. May’s cunning plan is no more than a statement of the obvious, but it means that Johnson, Gove, Fox and Davis accept that the UK will stay in “a” customs union with the EU beyond 2020.

This week’s meeting did not decide which of the two customs options would apply after that. That heat will be turned up later. When I first used the frog-boiling analogy, before the Chequers away day in February, I naively assumed that meeting would decide the question. But this is slow cooking taken to an extreme.

By this, the prime minister has earned the continuous scorn of the commenting classes and provided Jeremy Corbyn with some of his best moments at Prime Minister’s Questions. How is it possible that two years after the referendum, the government still hasn’t decided what sort of Brexit it wants? How can the government negotiate with the EU when it is so busy negotiating with itself?

Well, prime ministers always face demands, from those with a professional interest in their failure, to “clarify their position”, or to “face down their internal critics”. Theresa May is not the best prime minister we have ever had, but she is not falling for those.

It is true that her attempt to keep her cabinet together has pushed the timetable for the final stages of the Brexit talks back to quite late in the day, and the legislative logjam in the House of Commons towards the end of this year could be fraught. But the talks would always have gone on until they hit the time constraint of treaty ratification before the March 2019 deadline.

From her point of view, it is better to keep the cabinet united for as long as possible. She is often urged to sack Boris Johnson, and so she should, but this is politics. It makes more sense for her to dare the foreign secretary to resign if he refuses to accept reality. So there he is, off to Argentina, out of harm’s way, while Jeremy Hunt, the health secretary, says: “He is a marvellous foreign secretary but let’s work as a team.”

What outstanding use of language. We do indeed marvel at the foreign secretary, and at his ability to stay in post. But Theresa May has the hard Brexiteers where she wants them: in the cabinet as we head for a soft Brexit.

I have no idea precisely how this is going to end. According to one account, it would take three years to prepare for even the simplest long-term option: that of being outside the customs union altogether (called “max fac” in the jargon). So that’s 2021. And it would take five years to prepare for May’s preferred option of being half in and half out (“customs partnership”). Which would be 2023. Another account says that nothing can be ready until July 2022.

You will notice that this is after 5 May 2022, which is the date of the next election.

The significance of this week, therefore, is that Johnson, Gove, Fox and Davis have signed up for a soft Brexit at least until the next election, simply because we will not be ready for anything else.

They have calculated that the important thing is to get out of the EU and argue about the details later. They are prepared to accept a temporary fix in the hope of getting a permanent deal to their liking later.

In other words, they are close to being well and truly boiled.