Keir Starmer faces a high-profile revolt over Brexit, with ‘more than 20’ MPs expected to defy him and vote against Boris Johnson’s deal.
MPs will vote tomorrow on whether to approve the eleventh hour trade deal secured by the Prime Minister on Christmas Eve.
Labour MPs are under orders to vote for the deal in the Commons.
But Labour MP Rupa Huq told Times Radio the number of rebels could be “more than 20”.
Former shadow chancellor John McDonnell and ex-cabinet minister Ben Bradshaw are among the signatories to a statement calling on opposition parties not to support the “rotten” agreement.
Sir Keir has said he will call on Labour MPs to support the “thin” post-Brexit free trade agreement, despite concerns that it will fail to protect many key economic sectors.
He argued that the alternative of ending the Brexit transition period on December 31 without a deal in place would be even worse for the economy.
However, his stance has upset some pro-Europeans in his party, who say they should not support a flawed agreement and should abstain instead.
The statement has been organised by Another Europe Is Possible and Labour For A Socialist Europe – both on the left – but has attracted support from both wings of the party.
As well as Mr Bradshaw, signatories include ex-cabinet minister Lord Adonis from the Blairite wing of the party.
From the left, Mr McDonnell is joined another former shadow cabinet minister, Clive Lewis.
The statement warns that it is the duty of the opposition to provide proper parliamentary scrutiny and to set out an alternative.
“That task gets harder if opposition parties fall into the trap of rallying around this rotten deal,” it said.
“We are witnessing an act of vandalism against our livelihoods, our rights and our horizons.
“We call on Labour, the Labour movement and other opposition parties not to support the Tories’ Brexit deal when it is put to a vote in the House of Commons.”
Other signatories are said to include former MEPs, councillors and local activists.
The DUP – which backed Brexit – has also said it will oppose the deal because the Brexit divorce settlement imposes customs checks between Northern Ireland and the rest of the UK.
Meanwhile, the self-styled “star chamber” of lawyers led by veteran Eurosceptic MP Sir Bill Cash and assembled by the European Research Group of Tory Brexiteers is expected to deliver its verdict on the deal.
Despite some reported misgivings over elements of the package, it is thought the group will be broadly favourable – although some are unhappy at the way the agreement, which runs to more than 1,200 pages, is being rushed through Parliament in a single day.
However, with Labour backing the agreement, it is expected to be passed comfortably on Wednesday.