LABOUR frontbencher Owen Smith has broken ranks with Jeremy Corbyn by calling for a new EU referendum.
The shadow Northern Ireland secretary said Labour should keep asking whether Brexit remains the right choice for the UK.
Mr Smith, who unsuccessfully challenged Mr Corbyn for the party leadership in 2016, insisted Labour needed to do more than "just back a soft Brexit".
Mr Corbyn has been careful to say that Labour is not seeking a second referendum on a Brexit deal, but has avoided completely ruling out such a vote.
Writing in The Guardian, Mr Smith said: "Given that it is increasingly obvious that the promises the Brexiters made to the voters – especially, but not only, their pledge of an additional £350 million 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."
Mr Smith said that remaining in the EU single market and customs union was the only way to meet the UK's commitments under the Good Friday Agreement.
"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.
"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."
Prominent pro-EU Labour MP Chuka Umunna described Mr Smith's comments as "excellent".
