The prime minister’s scheme to stay in the customs union indefinitely demonstrates both Boris Johnson’s impotence in the Cabinet and her own impotence in the Brexit talks.

The foreign secretary was “outgunned” when Theresa May bounced him into agreeing this proposal on Tuesday. He must be mad as hell because the prime minister’s scheme means following EU tariffs beyond the transition period, which was supposed to end in December 2020. The idea is to avoid border mayhem because the whizzo technology the government hoped would solve the problem can’t be magicked up in time.

May says we’ll still be able to cut trade deals. But how can we do that if we have to follow EU tariffs?

Striding the world like a latter-day Walter Raleigh was supposed to be one of the big benefits of Brexit. Like so many of Johnson’s promises, it was based on fantasy. We have much more clout in global trade as part of the world’s biggest trade bloc than we would on our own. That said, if we can’t clinch trade deals, Brexiters will be asking what’s the point of the whole goddamn business.

Their rage must be reaching boiling point because they know that May’s concession on tariffs isn’t her last. She was told by the Irish leader at a summit in the Balkans yesterday that staying in the customs union won’t be enough to avoid border controls. We’ll also need to follow many of the EU’s single market rules. Leo Varadkar said: “I very much emphasised that resolving the issue of a hard border requires more than customs.”

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And that’s not all. In return for a longer transition, the EU may insist on “full acceptance of single market rules, regulators and courts”, not just some of its rules, according to the FT. That would mean also extending free movement of people and being forced to agree to “perpetual UK budget contributions”.

Finally, May’s hopes for a “time limited” period in limbo land could be dashed. The EU could insist that any backstop deal to avoid border controls in Ireland is a lasting guarantee. This means that, if the Brexiters’ magical technology never works, we would be stuck in customs purgatory year after year.

The prime minister is snookered because she knows it would be crazy to quit the EU without a Brexit deal – and the EU is adamant that there’ll be no deal without a solution to the Irish border. Meanwhile, the Brexiters are snookered because they can’t get rid of her. Half of Tory MPs need to vote against her in a confidence vote to trigger a leadership contest – and they don’t have the numbers.

Johnson didn’t think any of this through when he campaigned for Brexit two years ago. May didn’t think any of it through when she triggered Article 50 last year. We are likely to end up with a really miserable deal. All the more reason for the people to get a vote on it.

Edited by Luke Lythgoe