The "abhorrent" possibility of border controls being re-established between the State and Northern Ireland in the event of a 'Brexit' has been raised by Tánaiste Joan Burton.

In a speech to the annual congress of British trade union GMB in Dublin last night, Ms Burton argued that Britain leaving the EU would be bad for Ireland and bad for Europe.

She said that would have undesirable impacts for both parts of the island of Ireland.

“Not that many years ago, there were customs posts and security checkpoints on the border between Newry and Dundalk,” Ms Burton said. “These days, motorists can pass freely from North to South.

"Workers can move easily between the two parts of the island. The all-island economy has benefited hugely from the Good Friday Agreement and the framework of our joint membership of the European Union. "

She said the State and its citizens would be loath to sacrifice that freedom.

“The idea of demanding passports at the Border between North and South is abhorrent to me, and I suspect it would be unacceptable to any Irish government.”

GMB is a general amalgamated union and one of Britain's largest with more than 700,000 members. It is affiliated to the British Labour Party.

Ms Burton said she could conceive of no circumstances where Ireland would leave the European Union.

Referendum

“It is a remarkable fact that no Irish politician of any substance has ever suggested that we should,” she said.

She said she respected British prime minister David Cameron’s plan to hold an in-out referendum and said the Government would assist Britain in terms of what she described as “reasonable” reform it sought within the EU.