The Brexit adviser to the UK opposition Labour Party, Keir Starmer, said Sunday that the party unanimously favored remaining inside a customs union with the European Union in order to cushion the potential economic blow caused by Brexit.

Starmer told the BBC that although an exit from the EU's current customs setup was inevitable with Brexit, the UK should negotiate a new deal that "will do the work of the customs union."

Read more: EU warns Britain of 'unavoidable' trade barriers if it leaves customs union

"It's really important for our manufacturing base," he said. "And nobody can answer the question how you keep your commitment to no hard border in Northern Ireland without a customs union.

"Crunch time is now coming for the prime minister because the majority in parliament does not back her approach to a customs union and ... will be heard sooner rather than later," Starmer added.

The announcement follows a letter published on Sunday in the UK's left-leaning Observer newspaper in which 80 senior Labour Party figures warned that leaving the customs union would be so damaging to the country's economy that Labour would be unable to carry out its ambitious reforms if it came to power.

Labour Party leader Jeremy Corbyn is expected to elaborate on his party's revised Brexit stance on Monday.

Read more: UK Brexit minister David Davis dismisses 'Mad Max' future fears

Pressure mounts on May

The policy shift finally gives the Labour Party a markedly different approach to Brexit than the one favored by Prime Minister May, who has repeatedly insisted that the UK will leave both the EU customs union and single market.

May's hard-line stance, however, has divided senior figures in her party and the Cabinet over what Britain's relationship with the EU should look like after it leaves the bloc in March 2019.

Read more: Theresa May — A dead woman walking?

Labour's position could now see the party join forces with "soft-Brexit" advocates within May's Conservatives when a vote on the customs union comes before Parliament after Easter.

Responding to the possibility that Conservative lawmakers could split from the party leadership in the upcoming vote, International Trade Minister Liam Fox urged his Tory colleagues to keep an "open mind," adding that their concerns would be addressed in a speech May is slated to give on the issue on Friday.

dm/cmk (AP, dpa, Reuters)

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