Anti-Brexit campaigners have brought traffic to a crawl on the main road between Northern Ireland and the Republic of Ireland.

A convoy of protesters staged a noisy motorway go-slow near Dundalk, Co Louth, on Saturday, using lorries and tractors to highlight the impact of predicted customs checks on the local economy.

As fears grow of a hard Brexit, the Irish government has begun contingency work to identify possible locations for checkpoints along the border with Northern Ireland.

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.

Since the end of the conflict traffic has passed largely unimpeded between the neighbours on what would be the UK’s only land border with Europe.

To highlight fears that a hard Brexit may stop such easy border crossings, a trailer-load of sheep going to market and passport-toting residents took part in a theatrical “checkpoint” staged to highlight the detrimental impact if new customs barriers were imposed.

A rusty Second World War-era bicycle placed alongside a mock customs hut reinforced the message that a hard border was a return to the past which Prime Minister Theresa May has been adamant she wants to avoid.

Traffic was brought to a near-standstill by the protest (Niall Carson/PA Wire ) (Niall Carson/PA Wire)

Local residents on the frontier between north and south said they were caught in the eye of a storm which could have a devastating impact on cross-border relations.

Kitchen maker and demonstration organiser for Border Communities Against Brexit, Declan Fearon, said: “We are really in the eye of the storm of Brexit and we intend to make sure that this does not happen.

“We never want to see this community going back to what it was before.”

Mock border officers from the UK and Ireland wearing traditional greatcoats waved down traffic in front of a stage customs hut.

Horns blared, truck drivers in the queue pretended to pull their hair out and waved pieces of paper supposed to be travel documents.

Lines of people with placards had gathered.

Vintage signs proclaimed “Stop: Customs”.

(Niall Carson/PA Wire ) (pictures by Niall Carson/PA)

Mr Fearon added: “The people here do not want to contemplate the reinstatement of spikes and roads being closed and of customs checkpoints and it looks like that is where we are going.”

He said protesters were trying to make their voices heard in Westminster and Dublin.

Theresa May and Brexit Secretary David Davis have pledged no return to the heavily secured border of the past for Northern Ireland.

But Mr Fearon said: “It seems as if Theresa May and the British Government have no intention of listening to us.

“They would not contemplate any assurances or guarantees that the Good Friday Agreement would not be injured or changed in any way as a result of Brexit.