The question, set less by Brussels than the logic of Brexit, is how the UK government can in one move leave the European union’s single market and customs while also maintaining the flow of trade and people on its one land border with the bloc in Ireland

The fact that the existence of the land border in question cost more than 3,600 lives over 30 years led to the British government in December 2017 restating its commitment to avoid “a hard border, including any physical infrastructure or related checks and controls”.

Avoiding a backdoor for smugglers into the single market is additionally regarded as essential by Dublin and the European commission, as is avoiding crippling extra bureaucracy on Irish businesses.

The so-called Irish backstop in the 585-page withdrawal agreement – to remain in place “unless and until” an alternative solution for keeping the border open is found – offers one solution by doing two key things.

First, Northern Ireland stays within the EU’s regulatory regime, and under direct jurisdiction of the European court of justice, so as to allow a single market for goods on the island of Ireland.

Second, the whole of the UK shares a customs territory with the EU to avoid any checks on goods both between the Republic of Ireland and Northern Ireland, and Northern Ireland and the rest of the United Kingdom.

But rejected three times by the Commons on the grounds that the UK could be tied into the backstop indefinitely, leaving the government unable to sign its own comprehensive trade deals, the withdrawal agreement is said by Boris Johnson, still the frontrunner in the Tory leadership battle, to be “defunct”.

What is the alternative? In recent days, Johnson has suggested that the EU and UK could give themselves more time to work on the problem by relying on “Gatt 24 or whatever it happens to be” to provide for a “standstill in our current arrangements”.

Under article XXIV of the general agreement on tariffs and trade, tariffs would remain at zero even under a no-deal exit on 31 October for up to a decade, it is said. The agreement could additionally leave the Irish border open while the two sides sought a new accommodation.

The problem for Johnson, in the words of the trade secretary, Liam Fox, is that this “isn’t true”. Article XXIV is only relevant if there is an an agreement in principle on a free trade deal. It gives the two parties time to turn an interim deal into a final one.

But the EU has said that the first and necessary step towards a trade deal is ratification of the withdrawal agreement. And the Irish prime minister, Leo Varadkar, has said that without a legally binding guarantee that a hard border will not reemerge there will be no withdrawal agreement.

In the light of this, interest has been aroused in a 201-page report published on Monday by a non-government organisation calling itself the Alternative Arrangements Commission.

Backed by two former ministers, Nicky Morgan and Greg Hands, it has suggested that by 2022 a solution could be in place using a mix of technology, trusted trade schemes, mobile checks on food and animals within a new joint Irish-British Sanitary and phytosanitary (SPS) zone, special economic zones to push customs checks away from the border and a certain amount of looking the other way.

The problems with it are legion. By imposing checks within a newly delineated border zone it fails the central task of avoiding new checks, and creates targets for terrorists in the new mobile veterinary vans. The burden of Brexit is put on Irish businesses. The exemptions on checks for many crossing the border will set off alarm bells for those concerned about the integrity of the single market.

But the central problem for Brussels is that the plan is theoretical.

There remains no certainty at all that the complicated IT systems, democratic consultation on the creation of new economic zones or negotiations with the European commission on the finer detail would be finalised by the end of the transition period of “standstill” relations.

The Irish backstop would then have to remain to guarantee the avoidance of a hard border. The Brexit logic remains unyielding.