THE Labour Party will support remaining in a customs union after Brexit.
Sir Keir Starmer, the shadow Brexit secretary, said the proposal was the only way to avoid a hard border in Ireland.
Sir Keir, who previously worked as a human rights advisor to the Northern Ireland Policing Board prior to entering politics, said Labour's front bench was "unanimous" after "many weeks of discussion".
Labour leader Jeremy Corbyn is due to outline the policy in a speech today.
The party will support a position which would see the UK leave the customs union in its current format but then negotiate a new treaty which would "do the work of the customs union".
He told the BBC: "Obviously it's the only way of realistically to get tariff free access, it's really important for our manufacturing base and nobody can answer the question how you keep your commitment to no hard border in Northern Ireland without a customs union."
"The customs arrangements at the moment are hardwired into the membership treaty so I think everybody now recognises there's going to have to be a new treaty - it will do the work of the customs union," added Sir Keir.
Shadow international trade secretary Barry Gardiner, who was a junior minister at the Northern Ireland Office, said that the UK and EU would negotiate trade deals together under the plans.
"Of course the customs union only deals with goods with any third parties, so the tariffs and the quotas that were applied to any third party country would be the same for the UK and the EU," he said.
"That's how a customs union works and vis-a-vis ourselves, there would be a free movement of goods within the border."
SDLP leader Colum Eastwood had previously written to Labour leader Jeremy Corbyn urging him to remain within the customs union and single market.
Mr Eastwood had warned that Brexit could potentially "dismantle the architecture of our peace process".
However, Liam Fox, the international trade secretary, dismissed the Labour policy.
"Labour say they want to join a customs union. What does that mean?," he asked.
"Is it like Turkey, which has a customs union but only in goods, not in agriculture, not in services, not in finance? Is that what we want for Britain? Will we take rules in certain sectors but not in others?"
Mr Fox said Prime Minister Theresa May would be setting out the cabinet's agreed vision of its future trading relationship with the EU in a speech on Friday.
He urged rebel Tory MPs to "have an open mind", adding that Mrs May would "deal with a lot of the reservations that they have".
