The Labour Party could force Jeremy Corbyn to dump his plan to push through Brexit if there is a snap general election, his spokesman has admitted.

All manifesto commitments would be decided by the usual “internal party democracy”, he acknowledged – not by the leader or his close advisers.

The statement opens up the prospect of senior party figures deciding Labour should back a Final Say referendum – or even adopt a pro-Remain position – before the country goes to the polls.

Mr Corbyn’s spokesman insisted he would “accept” any decision – despite his pre-Christmas vow that Brexit would go ahead if he won an election before the 29 March departure day.

Last month, the Labour leader vowed to defying growing pressure to back a fresh referendum, insisting he would, as prime minister, head to Brussels to try to strike softer exit terms.

“You’d have to go back and negotiate, and see what the timetable would be,” Mr Corbyn told The Guardian.

The comments triggered a furious backlash from many Labour members, who are demanding a special conference to put power in the hands of activists.

Mr Corbyn’s spokesman, speaking to journalists, said Labour was still “committed to respecting the result of the referendum”.

However, he acknowledged the current policy, to renegotiate a better deal – with customs union membership and a “strong” single market deal – was only the position “at the moment”.

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“What our policy in a general election would be would obviously be decided by our internal party democracy,” the spokesman said.

“The manifesto that any Labour party stands on is always decided by the democratic procedures. It’s set out in our constitution – that’s a fact.”

Clause 5 of the constitution states that, when Labour is in opposition, various strands of the party must decide “which items from the party programme shall be included in the manifesto”.

They are: the national executive committee, the shadow cabinet, the parliamentary Labour party’s committee; and the chairman and vice-chairmen of the national policy forum.

The spokesman said Mr Corbyn would not seek to “overrule” the clause 5 decision and, asked if he would stay on as leader even if he opposed, he replied: “Of course.”

In December, asked if the paralysis in parliament made the case for a fresh referendum Mr Corbyn replied: “I think we should vote down this deal. We should then go back to the EU with a discussion about a customs union.”

Today his spokesman refused to be drawn on whether Labour would support an extension of the Article 50 process, to allow either an election or a referendum,

“We are not pressing for an extension to Article 50, but, if that has to happen, that’s the responsibility of the government.”

But in the Commons chamber, Sir Keir Starmer, Labour’s Brexit spokesman, said a pause beyond 29 March “may well be inevitable”.