With the United Kingdom set to leave the European Union, the re-introduction of some form of border controls between Northern Ireland and the Republic is, perhaps, inevitable.

In particular, after Prime Minister Theresa May confirmed that the UK will be leaving the single market, few can be surprised to hear that the Irish Revenue Commissioners have begun identifying possible locations for customs checkpoints.

Internal government documents, whose contents were reported in yesterday's Irish Examiner, are said to examine possible sites in Louth, Monoghan, Cavan, Leitrim, and Donegal.

Yet if the news is not surprising, the prospect of a reinstated border still has the potential to alarm – another reminder of the unavoidable impact of Brexit on these isles.

According to the Donegal Daily, Sinn Féin TD Pearse Doherty has called the proposals “deeply worrying”.

“This is a major cause for concern for the island of Ireland as a whole, but particularly for counties along the border where communities there have such close social and economic links. “The re-introduction of full customs checkpoints would cause considerable economic upheaval, and poses a very real threat to our economy and to employment on this island – both north and south.

Concerns have already been raised about services which may be threatened by Brexit. Cross-border health schemes that currently give Irish patients NHS access, for instance, may be at risk, according to UK government documents leaked to the Times.

For those in the border counties, however, the concerns are not only practical.

Although systematic customs checks were abolished in 1993, with the creation of the single market, it was not until the terms of the 1998 Good Friday Agreement were implemented that British military checkpoints were removed from the Irish border. The last major structures were removed in 2007.

Nowadays, road travellers from the North may not even notice they have crossed into the Republic until the first bilingual road signs appear.

Yet the border still looms large in the local imagination. Darran Anderson, the author of Imaginary Cities, is from Derry-Londonderry, and grew up with a military checkpoint at the end of his street.

“The psychological dimension, and the political reverberations from that, shouldn't be overlooked," he tells me.

“The free movement of people across the border has encouraged plural senses of identity and belonging. It was never quite the European cosmopolitanism that some claimed but it was much looser than the traditional 'us and them'. With a reinstated border, we face a situation where the young in particular are expected to return to old identities and allegiances to which they've never really subscribed. Other borders, beyond the physical, risk being reinstated.

Although politicians would no doubt point out that there is a big difference between watchtowers and a routine customs stop, for some, even these proposals represent a worrying step backwards.

“Even if it does occur with minimal disruption, how long will it stay that way?” Anderson asks. “The head of the Police Federation for Northern Ireland has expressed concerns that border posts would be 'propaganda gifts' and 'sitting ducks' for rogue Republican groups, adding that attacks are ‘highly likely.’

"Should those occur, and security be stepped up as a result, it is very easy to see the border becoming re-militarised and the reassurances going the way of the Leave campaign's NHS funding pledge.”

Brexit secretary David Davis has promised that there will be no return to a “hard” border.

Last week, the House of Commons voted down a proposed amendment by the Social Democratic and Labour Party which would have guaranteed that the terms of the Good Friday Agreement be considered during negotiations to leave the European Union.

Speaking after the vote, Ulster Unionist Party MP Tom Elliot re-iterated comments made by the Irish ambassador, Daniel Mulhall, stating that the Irish government has “absolute determination” that the 1998 agreement will not be impacted by Brexit.

But the work on the Irish border suggests the practical side of Brexit may overrule the political principle.

The Irish Revenue Commission have been approached for comment.