Promises from British Brexiteers of a seamless or soft Irish border are almost worthless. They have other priorities, and anyway it depends on negotiations involving 27 other states, crucially including the Irish Republic. A Northern Ireland majority, including many unionists, voted 56% Remain; few Leavers want the return of a hard border; and most people in the south are strongly opposed. But there will probably be a hard border. The only question is where.

The land border between north and south leaks like a sieve. It comprises the borders of 17th century administrative counties, meanders around for 300 contorted miles, goes through towns and villages, local communities, farms and occasionally houses – front door in one state, back door in the other. Even when highly militarised during the Troubles with 200 border-crossing roads made unusable it was still a leaky border. It is virtually useless for controlling an inflow of immigrants which was apparently the main reason for Brexit. So the real and hard border will actually be the sea around the island of Britain and the ports and airports connecting with the island of Ireland, though with very important revisions if there is an independent Scotland, and it remains in the EU.

For controlling freight movements Ireland's border depends on whether free trade can continue between north and south under some hybrid EU arrangement (for example, the north remaining in the customs union). That would limit the Brexit damage to their substantially integrated economies, and also locates the hard border for goods at the ports and airports connecting Ireland and Britain. These already have physical infrastructures for controlling freight separate from people, unlike Ireland's land border. Controls here would mean costly delays and clog up border roads for the thousands of people who regularly criss-cross in both directions to work, study, shop, socialise, or use health services.

A supposedly hard land border would inevitably prove leaky for goods as well as people, with the south getting smuggled food and other commodities not up to EU standards. Not everyone wants borders but only smugglers want leaky, uncontrollable ones. So functionally having the real or controllable border at the ports and airports makes sense for both parts of Ireland and for Britain and the EU. It also makes sense for political reasons. Two decades of an 'invisible border' have meant a huge increase in regular crossings and in people living their lives on both sides. Any attempt to re-impose a hard border would be highly disruptive and extremely unpopular,
not only in local border communities but more widely. There would inevitably be widespread popular resistance and civil disobedience.

More ominously, it would undermine the 1998 Good Friday agreement. The 'peace process' has been reliant on cross-border institutions and the explicit minimising of the border; the shooting war was stopped on the promise that Ireland could be reunited politically by peaceful means if people voted for it in a border poll. Reimposing a hard border would wreck this more or less successful strategy. The only people to benefit would be paramilitaries who prefer violent means.

Building land border installations would be an open invitation for the Republican dissidents to revive the IRA's 1950's 'Border Campaign' of attacking border posts. That campaign was an unpopular failure, but a similar campaign today might increase their support, which in turn might increase loyalist paramilitarism. While a full return to the Troubles is unlikely, there could be 'mini-Troubles' which escalate.

Avoiding all the various threats by displacing the hard border to ports and airports won't be easy. Defining and achieving the crucial 'hybrid EU arrangement' for north-south relations faces substantial problems. The administrations in Belfast and Dublin are currently problematic, not to mention the one in London. Northern power-sharing collapsed and the leading unionist party, the DUP, is pro-Brexit and out-of-step with the majority. That puts even more onus on the Dublin government, but foreign minister Charlie Flanagan has argued against special EU status for Northern Ireland (in mistaken deference to British Brexiteers?), on the peculiar grounds that it would deflect from Ireland's uniqueness.

But uniqueness is indeed a very strong reason for a special hybrid solution and the EU is well aware of it. Having poured millions into the cross-border 'peace process', it wouldn't want a hard border resparking Troubles. And it can accommodate hybrid solutions and anomalies: an EU member state, Denmark, contains Greenland which is not in the EU, while some countries outside the EU are in the EU's single market or its Schengen travel agreement.

The Dublin government must be directly involved in the EU negotiations – there's no formal provision for that but nothing to stop it either. While the EU does not owe Britain any favours, it certainly owes the Irish Republic. It has been 'EU loyal' to a fault; it is the only EU state sharing a land border with British territory, it will suffer more from Brexit than other EU states, and will continue to be most closely tied to Britain. Conversely, Northern Irish people qualify for Irish citizenship, they will constitute a major geographical
concentration of EU citizens living outside the EU, and can demand to be taken into consideration. If the EU is politically smart (always a question), it will reward its supporters – and that should extend to the 62% of Scots who voted Remain and perhaps to an independent Scotland staying in the EU.

If Irish nationalists were smart – sometimes another big 'if' – they'd avoid the usual reheated and over-heated rhetoric about a 'united Ireland'. The reckless Brexiteers may eventually wreck the union with Britain, but the new and immediate challenge is not about politically unifying Ireland. Campaigning for a border poll would stop many unionists from joining the struggle against the reimposition of a hard land border, and probably prove a premature distraction. Instead we should concentrate on retaining the
'invisible' border and that needs the support of unionists as well as nationalists.

James Anderson is emeritus professor of political geography in the Mitchell Institute and a founding-member of the Centre for International Borders Research at Queen's University Belfast

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