Jeremy Corbyn. | Leon Neal/Getty Images Labour members raise pressure on Corbyn over Brexit stance More than 80 party figures say Labour’s plans can only be achieved by staying in the single market.

A group of more than 80 senior Labour Party figures on Sunday urged leader Jeremy Corbyn to declare that the U.K. should stay in the EU single market.

The single market “is more than a free trade zone between EU countries. It is a framework of rules — including on employment rights, consumer and environmental standards — that protects people from the worst excesses of globalisation and unfettered capitalism,” they said in a letter published by the Observer.

The group of MPs, MEPs, peers, council leaders and trade unionists say that “we can only properly fund local services, schools, hospitals, social care and international development if our businesses thrive and our economy grows.”

The letter comes as Corbyn prepares to announce a major shift in policy that is expected to commit the party to backing permanent membership of a customs union with the EU.

According to the Guardian, his speech “will open a far clearer divide between Labour and the Tories over Brexit and raises the possibility that the party’s MPs could join forces with pro-EU Tories, the SNP [Scottish National Party] and the Liberal Democrats to inflict damaging defeats on Theresa May in a series of Commons votes in the spring.”

May will set out her Brexit agenda in a major speech next week following a meeting of the Cabinet.

On Friday, the president of the European Council, Donald Tusk, said that “if the media reports are correct, I am afraid that the U.K. position today is based on pure illusion.”

He was speaking after a meeting of senior British government ministers who reportedly agreed on the phrase “managed divergence” to describe the nature of EU withdrawal.

That position broadly matched the one set out by Brexit Secretary David Davis in a speech in Vienna on Tuesday — for a so-called three baskets approach of “managed divergence,” where Britain takes back control over rules and regulations, but maintains the equivalent high goods standards of the EU in key areas to protect trade and jobs.