PETER Mandelson, a former Secretary of State for Northern Ireland, has called for the UK to remain inside the single market and customs union following Brexit.
Lord Mandelson, who is also a former European Commissioner for Trade, said that continued membership of both could avoid a hard border and ensure political stability in the north.
In a speech to the British-Irish Chamber of Commerce at its annual gala dinner in Dublin, Lord Mandelson said that it was time to "live up to and safeguard what was achieved 20 years ago".
"We are talking about hundreds of thousands of people, directly and indirectly, who depend in their businesses, their jobs and their education on the borderless link between south and north," he said.
"That is a measure of the risk if we get things wrong. People in Britain will be dismayed if the Good Friday Agreement and the peace it has brought is damaged."
Lord Mandelson said that "cumbersome, unworkable or untested border controls" were "not a substitute" for keeping the island of Ireland in a single customs union.
"All this could be avoided if the British government took the sensible decision, on leaving the EU, to remain in the single market or at least the customs union. Or preferably both."
The Labour peer, who was Secretary of State for Northern Ireland between 1999 and 2001, said that people are "hugely better off in the single economy that has emerged across the island of Ireland".
He said: "We should not see the border back. We do not want to see a new smuggling industry taking off replacing the legitimate trade that takes place now. We do not want to see peoples' daily lives disrupted.
"In the case of the Northern Ireland border we need something different even if the solutions don’t fit the way we conventionally do things."
The former cabinet minister also criticised the UK government's approach to the talks and the overall negotiation process.
Discussions which have seen the UK and EU teams at odds over key issues are "being conducted by people largely talking past each other as if on two separate planets, as different as Mars and Venus," Mr Mandelson said.
"The government cannot, as they repeatedly claim, have the 'exact same benefits' of the single market when outside it, as we enjoy today inside it.
"A year ago, I was a passionate Remainer but I could live with the result if in the cabinet in London they would respect the views of the 48 per cent of us who do not want a complete break with Europe," added the Labour veteran.
Lord Mandelson's remarks on the border were welcomed by Eoin O'Neill, the President of the British-Irish Chamber of Commerce.
"We believe that a tailored customs arrangement between the EU and UK would best protect the interests of business on these islands and provide a pragmatic basis for the UK government to meet its own objectives with regard to Brexit," he said.
