The European Union has invited Prime Minister Theresa May to resolve the border issue, about 500km, between the Republic of Ireland, an EU member and the province of Northern Ireland, which is part of the United Kingdom.

It is the only land border between the United Kingdom and the EU except of course Gibraltar.

Theresa May stated that the whole of the United Kingdom will leave the EU single market and the customs union.

The European Union has instead insisted that the negotiations can not go on unless Britain agrees on the customs regulations, they must remain unchanged on both sides of the Irish border once the Brexit has been carried out and moreover, Brexit should not lead to the creation of a "Hard Border" with Northern Ireland.