Customs outside Newry, Co Down on the main Dublin to Belfast Road in the 1980s. Picture by Pacemaker Press

CUSTOMS checkpoint locations are already being scouted along the north-south border by the Republic's government under contingency plans in the wake of Brexit.

It has been reported that possible sites for customs posts including 'red and green channel' facilities are being identified in Donegal, Cavan, Monaghan, Leitrim and Louth.

The M1 between Belfast and Dublin will also be a focus for checks if a full hard border is enforced when the UK leaves the European Union.

The extent of the south's Brexit planning is said to be contained in internal government documents which was reported in yesterday's Irish Examiner.

Brexit teams have been formed in all departments and contingency planning is examining all scenarios.

The documents read: "This work includes technical feasibility of a range of possible outcomes and also the serious political implications that a border may bring."

Revenue Commissioner officials have also been engaged to determine all "legal and practical implications of a range of scenarios".

This includes identifying locations for border checkpoints with 'red and green channel' facilities – the 'red channel' being for those with goods to declare and 'green' for nothing to declare.

A special Brexit cabinet has also been formed with various government ministers including Taoiseach Enda Kenny, Tánaiste Frances Fitzgerald and finance minister Michael Noonan.

The south's strategy to cope with Brexit involves consulting with stakeholders and the public, and engaging with the EU and other member state governments.

The plans emerge despite public statements from the government including Taoiseach Enda Kenny who has warned that "any manifestation of a hard border" will have "very negative consequences".

British prime minister Theresa May has previously said she wants to see a "seamless, frictionless border" when the UK leaves the EU.

She has also said the British government does not want to see a "return to the borders of the past".

Customs posts were a common sight during the Troubles along the 300-mile border between Northern Ireland and the Republic.

There were just 20 border crossings open during the Troubles, but today there are 260 border roads with all of those blocked during the years of conflict now back in use.

One former UK custom officer last week warned that policing the border now is "mission impossible" due to the hundreds of roads now criss-crossing between north and south.

In last June's historic EU referendum, 56 per cent of voters in Northern Ireland backed Remain but overall 52 per cent in the UK voted Leave.

Mrs May plans to invoke Article 50 next month, triggering two years of formal EU divorce talks.