A month ago when he finally entered Downing Street Boris Johnson declared that, come what may, the UK would leave the EU by 31 October.

In the weeks leading up to his formal confirmation as Prime Minister some commentators of note suggested that this most mercurial of politicians was almost bound to renege on this promise. He was uniquely untrustworthy they said. But with the appointment of Dominic Cummings as his senior aide his intent could not have been clearer. If we don’t leave by Halloween Boris is toast. Johnson had painted not so much a red, as a crimson line. Nothing that has happened since has hinted at any deviation from this position.

His opponents in parliament have certainly taken him at his word and have rallied to defy him but are still shorn of a viable plan. Meanwhile Boris has drawn another crimson line. He has insisted that any new deal is wholly dependent on the EU jettisoning the so-called Irish backstop.

The backstop is an ingenious concept, one that has had bestowed upon it a special reverence during these negotiations. It was included in the doomed Withdrawal Agreement to safeguard an open border between Northern Ireland and the Republic of Ireland should the UK and the EU not reach an acceptable trade arrangement after an agreed transition period. It was conceived in December 2017 and almost immediately became an immutable symbol of good faith for both sides, constantly invoked by countries who had never previously much concerned themselves with the Good Friday Agreement and its aftermath.

However the adoption of backstop had a vulnerability built into its birth. It required and was dependent on receiving the consent of the UK parliament. Without this and with the Article 50 clock ticking – albeit with sporadic enforced stops – the very event that it was designed to prevent in the medium term would suddenly unavoidably appear in the headlights. So it has come to pass. I am not sure even the Germans have invented a name for this calamitous turn of events. The Withdrawal Agreement with the backstop baked in was defeated three times in the Commons and now our new PM has declared the Withdrawal Agreement a dead duck unless the Irish backstop is jettisoned.

Which is were our friend Dom Cummings comes in.

During the 2010 General Election campaign I recall a conversation with a veteran former Tory MP who had stood at every such election since before I was born. He couldn’t remember a single campaign in 50 odd years when Labour had not devoted a day to “the Tories are going to destroy the NHS” pitch to voters. Six years later Vote Leave painted a red bus with a £350 million a week for the NHS message emblazoned on its side and had it move around from one solid Labour constituency to another. The chutzpah behind this was gob smacking but its impact was devastating and ultimately decisive. Cummings had intuited the lessons of 50 years of general election campaigns and in an act worthy of Sun Tzu deployed the strengths of his opponents against them. Indeed it worked so well that we are likely to be leaving the EU before we turn the clocks back.

For the NHS in 2016 read the backstop in 2019. If the EU27 fail to move on the backstop designed to stop a “hard border” in two years they will need to erect one in two months.

Once again it seems Dom Cummings may have sensed the solemnity and steadfastness of his foe’s position and deployed it against them.

No one knows if there is an acceptable alternative solution to the problem that the backstop was supposed to sort – and the consequences of not finding one are truly unsettling – but we are about to find out both whether those who said they could never countenance a hard border in Ireland really meant it and if Dom Cummings has exposed the EU Achilles heel.