THE Irish backstop. The mystery wrapped in an enigma. The Schleswig-Holstein Question du jour. The entire three-years-long Brexit process has been reduced to the tedious issue of unstopping the backstop.

That’s what this week’s hectic round of mini-summits with Emmanuel Macron and Angela Merkel was all about.

The Withdrawal Agreement seems done and dusted, at least in Boris Johnson’s imagination, provided a way can be found to prevent a hard border b*****ing up the peace of the province.

The Prime Minister, intoxicated by his own ebullience, has promised to deliver a solution in 30 days.

A bit of “oomph” is all that is needed. Some positive thinking, and a bit of foot-on-the-table bonhomie. A hey and ho and a hey nonny no.

But he knows, and they know, and everyone else knows that this is prime Brexit bull. There is no way to avoid a border in Ireland, not least because there already is one: 310 miles of winding country roads with around 500 crossing points.

It has been there since the partition of Ireland following the wars of independence 100 years ago.

As my colleague Neil Mackay recounts in today’s The Herald on Sunday (Page 22), it was a focus of violent discontent for 80 years until the Good Friday Agreement put the border, like the guns, beyond use.

The border became irrelevant after 1999 because both Ireland and the UK were part of the European Union – the customs union and the single market.

This meant that there were no tariff barriers and no regulatory issues impeding trade. The border became a mere line on a map, of interest only to historians and superannuated Irish nationalists.

Britain is now leaving the customs union and the single market. But Boris Johnson insists that there should still be no hard border.

The Prime Minister announced in Paris that Britain “would not be erecting any physical border checks” after Brexit. He gave this assurance also to the Irish Taoiseach Leo Varadkar privately a fortnight ago.

This is a bluff, of course. A way to make it appear as if Brussels is to blame if and when any hard border emerges.

But what if Brussels calls Boris’s border bluff? What if the European Union simply says: fine, if Britain doesn’t wish to impose tariffs on goods imported from the 27, then who are we to complain? No enforcement of British product standards?

Fine by us. No sanitary and phytosanitary checks on animals, plants and foodstuffs entering the UK via Ireland? D’accord. Unrestricted entry for German cars? Vielen dank. The EU may slap 30% duties on British cheese, but if we are happy to have the UK cheese industry destroyed, then that is our choice.

Similarly, Conservatives may be unhappy about migrants entering the country by the Northern Ireland backdoor, but perhaps no-one will notice.

Scottish fruit farmers may start setting up recruiting offices in Belfast to hire cheap immigrant labour.

If Britain is happy to turn a blind eye, why would the European Union object? Of course, borders look both ways, and the EU wouldn’t want to allow uncontrolled imports of food and livestock from Britain when we leave the single market.

They don’t want those chlorinated chickens, hormone-fed beef and GM crops being imported to the European Union willy-nilly.

The EU has spent the last half-century managing the immense border of the customs union, encompassing two million square miles and 500 million people. Do we seriously think that they would be unable to manage the flows through the Republic of Ireland, an island of five million?

The assumption has always been that there would have to be a two-way border in Ireland. But the European Union needs only police exports from the air and shipping ports. It could treat Ireland as as if it were already united for economic purposes. It would be a backstop, but not as we know it.

There is already a common travel zone in Ireland which has existed since the 1920s. The North and the South are a common regulatory zone at present, a legacy of EU membership.

If Brussels uses its skill in border management, it certainly could surely find ways to prevent produce of UK origin from leaking into the European Union by rigorously scrutinising exports from the Republic.

By regarding the island of Ireland as a unified space, the border would become Britain’s problem.

The DUP MPs might be uneasy about this solution because it would rather look like a prelude to a united Ireland. It probably would be, because it would involve a kind of all-Ireland common market.

But this needn’t be explicit. Boris Johnson could give an assurance that Britain will not regulate trade between the North and the UK mainland.

The great advantage of Johnson doing the Brexit negotiations is that he led the Leave campaign. There is no suspicion that he is a closet Remainer, like Theresa May.

He is also a Unionist – Minister for the Union, no less. If he strikes a deal with Brussels that covers the Irish backstop in a mountain of fudge and obfuscation, he might just get away with it. It is a matter of historical fact that the European Union never wanted the Irish backstop in the first place.

It was originally a British proposal. Theresa May’s customs partnerships and common regulatory rule books looked like an attempt to retain the benefits of the single market without being a member of it. The last thing Brussels wanted was for this hybrid arrangement to provide a template for other countries wanting to get into the single market under the wire.

The backstop really was intended only to be temporary – until a comprehensive trade deal was negotiated, or until Britain found “technological solutions” to managing the border. Magic eyes, drones, warehouse checks, mobile phones and digital certification.

The European Union’s main interest now is in getting the Withdrawal Agreement through and Britain paying the £39 billion divorce bill.

Most of the issues relating to Britain’s departure have been resolved. Only the backstop remains. Brussels could discreetly agree with Boris Johnson that all of Ireland, for regulatory purposes remains a country with no border. Would Leo Varadkar accept this?

There would be problems dealing with the £3bn worth of produce imported into the Republic from Northern Ireland every year. But is this any different to what would have to happen if Ireland were politically reunited?

Moreover, the Republic could become an attractive destination for foreign firms seeking unrestricted, border-free access to the UK market. It might mean Britain giving up any “selfish or strategic” interest in the North as the Downing Street Declaration put it in 1993.

But the ties that bind the UK to the province have long since eroded. Nearly two-thirds of Conservative voters say they would be happy to see the Union ended if that is the price of Brexit.

Brussels should say: bring it on.