A shadow cabinet minister has broken ranks with official Labour Party policy to call for another Brexit referendum.
Shadow Northern Ireland Secretary Owen Smith said a vote should be held when talks with the EU have concluded.
He also called for Labour to back membership of the EU single market, in an article for The Guardian.
Jeremy Corbyn last month announced Labour wanted the UK to be a permanent member of a customs union with the EU after Brexit.
But Mr Smith, who unsuccessfully challenged Mr Corbyn for the Labour leadership in 2016, said that was not enough.
“If we insist on leaving the EU then there is realistically only one way to honour our obligations under the Good Friday agreement and that is to remain members of both the customs union and the single market,” he said in his article.
“I’m pleased my party has taken a big step in this direction by backing continued customs union membership, but we need to go further.”
He argued that Labour “needs to do more than just back a soft Brexit or guarantee a soft border in Ireland”.
“Given that it is increasingly obvious that the promises the Brexiters made to the voters – especially, but not only, their pledge of an additional £350m a week for the NHS – are never going to be honoured, we have the right to keep asking if Brexit remains the right choice for the country.
“And to ask, too, that the country has a vote on whether to accept the terms, and true costs of that choice, once they are clear. That is how Labour can properly serve our democracy and the interests of our people.”
Labour frontbencher Owen Smith backs another EU referendum}