LEN McCLUSKEY warned the Labour leadership today against “sitting on the fence” by ordering the party’s MPs to abstain in any vote on a post-Brexit trade deal.

The general secretary of the Unite union — Labour’s biggest donor — insisted it would be “completely wrong” for the party not to vote one way or the other should Britain and European Union agree on a deal.

His intervention coincided with Environment Secretary George Eustice saying that the negotiations aimed at reaching such an agreement are entering the “final few days.”

Shadow ministers insisted in television interviews yesterday that they want Prime Minister Boris Johnson to secure a deal, while adding that the party would reserve judgement on how it would whip MPs to vote until the details were revealed.

Shadow home secretary Nick Thomas-Symonds acknowledged on Sky News’s Sophy Ridge On Sunday that abstention was among the options available.

Given that there a differing views in Labour ranks on the best tactics, party leader Sir Keir Starmer is likely to find unity on the question hard to achieve.

Mr McCluskey said that Sir Keir needs to “win the trust of the red wall seats” and voters who backed Leave in the 2016 referendum, and be seen “not to be standing in the way” of what people supported in last year’s general election.

He told Times Radio: “On the other hand, if it’s a thin deal, which I suspect it will be, if indeed we get a deal, he needs to also be in a position in six months if things are going wrong to be able to attack the government without then being regarded a hypocrite because he voted for the deal.”

Mr McCluskey said that he expects a deal to get through Parliament.

He added: “Frankly, Labour needs — on the most important issue of the day — not to be seen to be sitting on the fence.

“The idea of an abstention, to me, would be completely wrong. I hope they’ve learned the lesson back in December that any confusion over this will be damaging to them.”

Former Labour prime minister Gordon Brown said on Sky News that he doesn’t think Sir Keir would make his decision “until he sees what the deal is.”

He warned that Britain could find itself in an “economic war” with the EU and United States if Mr Johnson fails to reach a Brexit agreement.