Tough choices will be needed to clear this logistical logjam

So what is the problem in Northern Ireland? The peace settlement is founded on a central ambiguity: Nationalists can opt to hold Irish citizenship (and only Irish citizenship) while Unionists can remain British. In essence, Nationalists and Unionists can live together in parallel constitutional realities.

By taking Britain out of Europe, Brexit collapses this core ambiguity: when Britain leaves the European Union in March 2019, the border between Northern Ireland and the Republic of Ireland will become an external border of the EU.

What is the UK solution?

London’s idea is to create an “invisible” border based on what the Government’s position paper on Northern Ireland calls a “highly streamlined customs arrangement” that would flow from a zero-tariff trade deal between the UK and the EU. The issue of local traders – say milk producers who raise cattle in the north but process their milk in the south – would be covered by a “local trade exemption”. The British argue that such trade is internationally insignificant and follows a long history of a certain amount of flexibility along the 310-mile border, which has some 300 crossing points.

So what is the problem with that?

Put simply, according to both Dublin and Brussels, it just won’t work. When the UK becomes a non-eu country, it will be free to cut trade deals with other countries. That could mean, for example, importing hormone-raised beef, genetically-modified food stuffs and chlorinated chicken from the US, all of which are blocked from the EU.

A free-trading Britain could also be free to seek competitive advantage. And however far the UK diverges, Ireland will have no choice but to “police” the border; indeed it will be legally obliged to do so by the EU.

What is the Irish solution?

The Irish solution is to make sure that regulations on both sides of the border between north and south do not diverge. This “all-island” solution, marked out in a recent European Commission discussion document that was leaked to The Daily Telegraph, would remove the need for a border, since regulations on both sides would remain the same. That would mean either the UK remains in the EU customs union and single market or the UK carves out a special status for Northern Ireland with the UK.

So what is the problem with that?

Well, assuming that Mrs May is not going to commit the entire UK to remaining in the customs union and single market, the only option is to give Northern Ireland special status.

That would, to all intents and purposes, make Northern Ireland a regulatory “exclave” of the EU, with the government in Belfast essentially required to mirror EU rules, which are in turn handed to Dublin from Brussels. It would also, by logical extension, require a border between the UK mainland and Northern Ireland. For Unionists, who see Northern Ireland as part of the United Kingdom, the creation of an “eastwest” border would be a profound act of betrayal by the Conservative Party.

Sounds like deadlock. What is going to happen?

Many businesses, political and constitutional analysts and officials closely involved in the technical aspects of any solution spoken to by The Telegraph, argue that the political and commercial logic of the issues thrown up by Brexit point to the creation of an east-west border.

Ultimately – perhaps after an extended period of transition which the Irish government has suggested – some form of unique new settlement for Northern Ireland seems inevitable.

What are the arguments in favour?

Whichever way you view Brexit and the Irish question, it unavoidably creates a constitutional issue for Northern Ireland. Putting aside the fact that 56 per cent of Northern Ireland inhabitants voted to remain, the Good Friday Agreement, with its dual citizenship and arrangements on policing and cross-border cooperation, already creates a “special status” for Northern Ireland that enables the peace process to work.

An east-west border outcome might be dismissed as impossible given that the DUP holds the key to Mrs May’s parliamentary majority, but ultimately the economic cost of a hard northsouth border may force a new reality.

Then there are the commercial and practical pressures: put simply, creating an east-west border to manage the UK’S future divergence from the EU is simply much easier than doing it north-south.

For a start, as one senior UK official

‘Ireland will have no choice but to police the border; indeed it will be legally obliged to do so by the EU’

privately observes, installing numberplate recognition cameras at Holyhead or Fishguard – where “no one is going to shoot the cameras out in the middle of the night” – is clearly easier than in the Irish borderlands.

Such camera technology on the UK side would be indistinguishable from other cameras.

Business groups also report their members would rather see an eastwest border, than an north-south one, even though the value of goods sent from Northern Ireland to Great Britain, at £10.7billion a year, is nearly four times the amount sent south.

What would that mean for the rest of Britain?

If the North in effect becomes a regulatory exclave of the EU, that raises the question of whether Dublin will effectively find itself representing the interests of part of the UK at the European Council. It would also prompt a much wider discussion about how the other devolved parts of the UK will relate to Westminster and Europe. If Northern Ireland is exempted from the consequences of an “English” decision to diverge from the European framework, how long before Scotland asks for its own special dispensation? The need to address the Northern Ireland question also goes to the heart of the debate currently roiling the Cabinet over how far the UK should really diverge. If UK consumers are against chlorinated chicken and GMOS then it may turn out that creating and managing an east-west border is not nearly as difficult as it seems. But as Wilbur Ross, the US trade secretary, made clear this month, if the UK wants a trade deal with the US, it must be prepared to reduce the “unnecessary divergence in regulation and standards” between the US and the EU. These are the tough choices that await the British public and their politicians.