The Irish Government has begun identifying possible locations for checkpoints along the border with Northern Ireland, as fears grow of a “hard Brexit”.

Preparations are underway for the return of a hard border – despite Theresa May’s insistence that the move will not be necessary even after EU withdrawal is completed.

Internal documents uncovered by the Irish Examiner showed officials in Dublin fears that full “red and green channel” customs points may be needed.

Those checks would be introduced in Louth, Monaghan, Cavan, Leitrim, and Donegal, with the M1 motorway between Dublin and Belfast also likely to be a focus for customs officials.

The move was then confirmed by Michael Noonan, the finance minister, in evidence to an Irish parliamentary committee.

Mr Noonan pointed out that both London and Dublin said they did not want to introduce a hard border, but that would require the agreement of the EU as well.

“Even though it is the intent of the two jurisdictions involved, we still have to get it across the line in Europe and that might be five or six years down the line,” he said in a later interview.

“The customs are looking at contingency, in the event of where the negotiations may land,” Mr Noonan added.

One minister told the Irish Examiner: “No one is aiming for a soft Brexit anymore, it is now about preparing for the worst.”

And Pearse Doherty, a Sinn Fein representative in the Irish Parliament who lives in the North, told the BBC checkpoints would be “devastating”.

He added: “This will absolutely crush certain sectors, particularly sectors along the border region. It will have a devastating impact in terms of the North.”

The documents pointed to a lack of clarity coming from Downing Street as the reason why the Dublin Government could not be more certain about the possible return of a hard border.

”When negotiations start, Ireland will be ready. We will negotiate hard and fair,” one stated.

Only one day earlier, Enda Kenny, Ireland’s Prime Minister, vowed to fight any attempt to create a fortified frontier, warning success was vital for the Republic.

But Mr Docherty suggested Mr Kenny was unaware of the contingency plans being made by his own officials.

The border in the island of Ireland has long been recognised as one of most problematic Brexit issues, with the potential to revive the tensions of the past.

During The Troubles, there were only 20 crossings, but there are now thought to be as many as 250 after the peace settlement brought the reopening of huge numbers of roads.

The Prime Minister’s determination to pull out of the EU’s single market and its customs union have raised the prospect of border checks becoming necessary.