The UK took a decisive step towards a no-deal Brexit when both aspirant successors to Theresa May made clear that they would not abide by the Irish backstop clause.

Both Boris Johnson and Jeremy Hunt committed to pushing aside the Irish backstop during a debate organised by the conservative media platform The Sun on Monday. The backstop is a clause set in place to protect the Good Friday Agreement in Ireland by protecting the freedom of movement for people and goods, avoiding the need for physical border infrastructure.

In doing so, the two Conservative frontrunners set an impossibly high bar for success in Brexit negotiations. The future prime minister of the UK must now persuade Dublin and Brussels to accept the possibility of a hard border between Ireland and Northern Ireland.

Mr Johnson has committed to never accepting the backstop and he is now followed by Jeremy Hunt. Johnson told the Sun on Monday that the backstop was devised in the UK as “an instrument of our own incarceration in the single market and customs union.”

“The deal that is going to get through the House of Commons, the deal that is going to get us out of the EU won’t have that backstop and that is what we are going to put right,” Mr Hunt said.

The EU has said it is not prepared to renegotiate the deal, but both Mr Hunt and Mr Johnson are promising to do so prior to taking the UK out of the EU on October 31st, with or without a deal. In the case of no deal, the UK would also withhold the so-called “divorce settlement” of £39bn.

The clear red line drawn by the two aspirant prime ministers on Monday led to a sharp drop to the pound on Tuesday, as a disorderly Brexit appears increasingly likely.

Eurosceptics claim that come November 1st, the UK could evoke Article 24 of Gatt, which would allow the UK and EU to maintain their current tariff-free trade while they negotiated a deal. But unlike the transition period envisaged in the Withdrawal Agreement negotiated by Theresa May, the UK would not be bound by new EU rules and would not be under the jurisdiction of the European Court of Justice.

Critics counter that Gatt Article 24 can only be applied if the two parties agree to the framework of a new trade agreement, which they have not and they are not likely to do so in a “no-deal” Brexit scenario.

The EU maintains that even if the UK does leave on October 31st, it would have to honour the £39bn settlement, keep the Irish border open, and respect EU citizens’ rights. For its part, the EU is willing to grand the UK a loose Canada-style trade agreement.