Irish politicians and diplomats are now finding themselves in an unholy alliance with pro-Brexit ideologues in the UK as they keep insisting that under no circumstances will there be any customs checks and border posts between Northern Ireland and the Republic of Ireland in the event of the UK quitting the European Union customs union.

The Tory election manifesto states: “Leaving the European Union also means we will be free to strike our own trade agreements with countries outside the EU.” This means the UK leaving the customs union, which would have very serious implications for Northern Ireland. On every EU external border with countries outside the customs union there are formal customs controls with the usual barriers and inspection buildings.

The former UK cabinet minster Owen Patterson, a committed Brexiter, told the BBC the Border would be like the one between the United States and Canada, with electronic customs clearance taking place so physical border checks are not needed. That is true for big transborder firms such as the big three auto makers, whose assembly and component plants are on both side of the Great Lakes.

Tariffs

But as anyone who has waited in line in a car to cross from the US into Canada or vice versa can testify, the border checks are real. The EU and Switzerland also have border and customs control posts, as do Sweden and Norway – the latter outside the EU customs union, while Sweden is a full EU member. According to the Norwegian embassy in London, there are staffed border posts and regular checks to ensure nothing comes into Norway that avoids the duties and tariffs required by law. Queues to cross from Norway into Sweden are the norm.

After months of being in denial can the powerful Irish lobby start to make clear that a full amputation of the UK from the EU single market and customs union is the final revenge of English nationalism on the people of Ireland?

Between Ireland and the UK’s six counties in Northern Ireland it may be possible to clear customs by electronic means for big-ticket firms such as Guinness or agribusiness giants. But there is a tariff of €1,670 on every ton of hard cheese imported into the EU, for example, and it is hard to see continental Europe’s cheese producers turning a blind eye to tariff-free cheese trade between EU and non-EU Ireland.

On the assumption that the UK will be leaving the EU customs union, the chief EU Brexit negotiator, Michel Barnier, says he has told the French government it must set up centres de dédouanement (customs-clearance halls) in every port on the French Atlantic coast that can receive a vessel that can transport goods from the UK.

Anti-Brexit campaigners with a mock customs hut at Carrickcarnon, at the border between Co Fermanagh and Co Cavan, to protest against the Brexit decision. Photograph: Reuters

The same will be true for Belgium, the Netherlands, Denmark, Spain, Germany and Sweden. The idea that the EU will insist on proper borders with all its other friendly neighbours such as Switzerland and Norway but make a special case for Northern Ireland is far-fetched despite the protests from Dublin and the blowhard Brexit statements in London that borders do not need controls – not the latter’s line, of course, when it comes to European citizens.

The days of Europe smiling forgivingly on Ireland’s tax laxity with Apple and other mainly US firms are over

One dramatic way of solving the problem would be for the UK to accept that all the island of Ireland was ring-fenced from Brexit and could stay in the EU customs union and single market. The politics and legal aspects of having a chunk of the UK in the EU even as mainland Britain becomes a “third country” and cut off from today’s trading and export access are probably insurmountable.

Per-capita GDP

The EU’s patience with Ireland’s exotic tax deals for foreign investment may now be running out. In terms of GDP per capita Ireland is the EU’s second-richest country according to the International Monetary Fund – $65,871 (€58,785) for each Irish citizen, compared with $40,412 (€36,065) for each Brit or $42,436 (€37,871) for each German. These figures flatter to deceive, as the Irish total GDP includes foreign firms who pay little tax.

Nonetheless, the days of Europe smiling forgivingly on Ireland’s tax laxity with Apple and other mainly US firms are over. So as Ireland grapples with how to handle Brexit and the frontier issue with the six countries still under UK suzerainty it faces a harsh dilemma. Do the Irish adopt Brexit language, blaming it all on Brussels? Or after months of being in denial can the powerful Irish lobby – its business leaders, superb diplomats, TDs and MEPs linked to European political parties, and the diaspora in Britain and the English-speaking world – start to make clear that a full amputation of the UK from the EU single market and customs union is the final revenge of English nationalism on the people of Ireland ever since they had the impertinence to follow America 140 years later and assert their right to be a free and independent nation no longer ruled by the English?

Denis MacShane is a former UK minister of state for Europe and author of Brexit: How Britain Will Leave Europe