Abstract
The UK’s withdrawal from the EU posed a significant challenge to the progress that had been achieved in Northern Ireland –one of the most impoverished post-conflict societies in Europe. Brexit could raise significant frictions along the territorial border between the two sides of Ireland and its all-island economy. If the UK had decided to remain in the single market and the EU customs union after Brexit, the vast majority of these challenges would have been avoided. However, since Theresa May’s Lancaster House speech, it became clear that the UK would not be part of the single market and the customs union after Brexit took place. So, the negotiations for the withdrawal of the UK from the EU were haunted by an almost unsolvable riddle. How could the UK and the EU keep the Irish border free of any physical infrastructure without jeopardising the integrity of the EU single market?