In Westminster Brexit politics, the threat of a Boris Johnson resignation has been the talk of the tea rooms almost since the day he joined the Cabinet as foreign secretary back in July 2016.

The poster boy for the campaign to leave the European Union feels it is his duty to interpret what Brexit means, and allies are quick to brief threats of his departure whenever he (or they) believe Brexit needs a course correction.

That resignation threat is again implicit in Johnson’s all-out attack in a Daily Mail interview on the “crazy” customs partnership plan: Theresa May’s preferred option for solving the post-Brexit customs dilemma.

“If you have the new customs partnership, you have a crazy system whereby you end up collecting the tariffs on behalf of the EU at the U.K. frontier,” he said. “That’s not taking back control of your trade policy, it’s not taking back control of your laws, it’s not taking back control of your borders and it’s actually not taking back control of your money either.”

It’s worth noting that we’ve been here before.

A fudge may yet be found to prevent either faction in Cabinet losing face, but if it can’t, Johnson will know all about the fable of the boy who cried wolf one too many times.

Cast your mind back to September when May was getting ready for her Florence speech that laid the groundwork for significant concessions in the Brexit talks. Ahead of the speech, Johnson published a 4,000 word article laying out his vision for how Brexit can “succeed mightily.”

There were threats — conveyed via “friends” — to resign if May gave up too much in Florence, although Johnson himself later denied them. And then after the speech, the foreign secretary laid out four Brexit red lines in an interview with the Sun newspaper.

Two of those red lines on single market access are still up for discussion in the Brexit talks but two concerned the now provisionally settled transition agreement. On its duration, Johnson got his way. He wanted not a “second more” than two years, although he may count himself lucky that EU negotiators were on his side in also wanting a short transition to fit with the current EU budget cycle — 21 months.

But on his refusal to accept “EU or ECJ rulings” during the transition, Johnson was less successful. British negotiators failed to get their way — beyond providing some political cover for May via a clause committing both sides to act in good faith and an EU agreement to consult on other issues.

Johnson’s government strode over his red line in March but the foreign secretary stayed put at his desk in King Charles Street. Why?

First, the compromise was forced at the negotiating table in Brussels rather than being the government’s policy and second, it took six months to breach Johnson’s red line — enough time for most people to have forgotten about it.

Neither of those things apply this time. The customs argument will likely come to a head in Cabinet in the next couple of weeks, and this is a tussle over the government’s starting position in negotiations — not what it will eventual accept.

A fudge may yet be found to prevent either faction in Cabinet losing face, but if it can’t, Johnson will know all about the fable of the boy who cried wolf one too many times.

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