Boris Johnson maintains he is preparing for a no-deal Brexit not because he expects or wants it, but to show he is ready to use the nuclear option.

If the EU 27 won’t reopen Theresa May’s “dead” withdrawal agreement and toss out the Irish backstop, her successor says he will, with a sigh, press the button on October 31.

The Prime Minister’s most senior EU adviser, David Frost, this week delivered the message in person to European Commission officials.

Chancellor Sajid Javid announced an extra £2.1bn for no-deal planning, and fuelled speculation about an emergency budget in early October by admitting the date was in flux.

Read more: Bank of England cuts growth forecasts and warns of impact of no-deal Brexit

Besides threatening to become a self-fulfilling prophecy, the strategy appears to be affecting the wrong audience.

The other EU nations are refusing to blink and say they won’t entertain abolition of the backstop.

Guy Verhofstadt, the European Parliament’s coordinator on Brexit, said increased talk of a no-deal would not “intimidate” the EU27, who had their own contingency plans ready.

For them, self-interest and the integrity of the EU single market take primacy over the UK’s decision.

Writing in the Guardian, he said: ”In the face of such irresponsible posturing, fare from feeling threatened, I fully expect EU governments to remain calm and keep their unity. Attempts to put pressure on ireland will only be met with waves of solidarity from the rest of the EU.”

He added: “We must not allow an injurious Brexit strategy, wrongly wrapped in an English flag, to harm us all.”

The markets are now pricing in an economic hit from no-a deal Brexit.

After days of decline, the pound fell to a new low on Thursday against the dollar, putting a damper on holidays by depressing an already lousy exchange rate.

Bank of England governor Mark Carney warned that no-deal appeared to be getting likelier, and would mean a further drop in sterling, lower GDP growth, and rising inflation.

The prospect is straining the Union, with politicians in Scotland, Wales and Northern Ireland railing against the idea on Mr Johnson’s UK tour this week.

Read more: Boris Johnson to chair first Brexit strategy meeting as no deal plans get £2bn boost

Worse, Mr Johnson’s strategy will embolden hardline Tory Brexiters.

Splashing cash on preparations as a gambit to win over the EU makes it far harder for the PM to back down at the last minute and request an extension or call a general election.

His MPs in the European Research Group will be able to cite the money, and especially an emergency budget, as proof the country is now ready for its great leap forward, whether they believe it or not.

Unless he throws up his hands and admits it was all for show, Mr Johnson will be unable to disagree.

The ERG will have a pistol in the small of his back, pushing him towards a no-deal – and he will have supplied the ammunition.