LONDON — Britain's main opposition party is poised for a significant policy change that could increase pressure on Prime Minister Theresa May to deliver a "soft" Brexit that maintains some formal economic ties to Europe.
There were clear indications Sunday that Labour Party leader Jeremy Corbyn will change course and advocate remaining in a customs union after Britain's departure from the EU to cushion the potential economic blow.
Keir Starmer, the party's Brexit adviser, told the BBC that Labour's leadership now is unanimously in favor of staying in a customs union. Corbyn plans to elaborate on the party's policy shift Monday, Starmer said.
Remaining in a customs union would greatly ease trade with the EU's other 27 countries after Brexit, which is expected to take effect at the end of March 2019, Starmer said.
He said it would also ease tensions in Ireland. The prospect of a hard border between Northern Ireland, which is part of the U.K., and the Republic of Ireland has raised concerns about the future of the Good Friday peace accord that ended decades of violence.
Starmer said remaining in a customs union was the only realistic way to get "tariff-free access" to the European market.
"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."
A policy shift by Corbyn would be significant because Labour lawmakers could join forces with advocates of a "soft" Brexit in the governing Conservative Party to pressure May, who already faces deep divisions within her own party.
If Corbyn and Labour clearly support a customs union, it would give the party a different approach from the one favored by May, who has said repeatedly that Britain will leave both the customs union and the single market.
Her own Cabinet has been badly divided on how best to pursue Brexit. May plans a major speech Friday to provide further details after a series of Cabinet meetings.
Pressures on Corbyn increased Sunday as more than 80 senior Labour Party figures signed a statement published in The Observer calling for Britain to remain in the EU's single market and the customs union after Brexit. The letter states that Britain's economy would be so damaged by leaving the single market and customs union that Labour would be unable to carry out its ambitious reforms if it comes to power.Comment on this story
The letter states that Labour's position in Parliament means it is in a position to prevent Britain from going too far in severing its economic ties to the other 27 EU members.
It says: "For the sake of building a better Britain and safeguarding those our party was founded to protect, we must grab this chance before it is too late. We will never be forgiven if we fail to do so."
The letter urges Corbyn to seek to keep Britain in the single market as well — but there are no indications he is ready to take that step.