From the beginning of their rebellion against Jeremy Corbyn, Labour MPs have always had a potential trump card to play: keeping him off the ballot. Legal advice to the party has stated that the leader would need the support of 50 MPs/MEPs (20 per cent of the total) to feature in any contest. When I asked a senior Labour figure yesterday whether Corbyn would require nominations, he replied: "The NEC [National Executive Committee] will ensure the rulebook is implemented." The party's 33-member governing body, which is expected to meet on Tuesday after Angela Eagle formally launches her challenge tomorrow, could vote to deny the leader an automatic place on the ballot.

Corbyn's interview on the Andrew Marr Show suggested he knows as much. While maintaining that he would be on the ballot as of right ("I've taken much soundings from lawyers. There are a lot of a lawyers about"), he also vowed to launch a legal challenge if the NEC ruled against him (“I will challenge that if that is the view that they take" he said when asked). Having lost the confidence of 81 per cent of MPs and the majority of Labour's 20 MEPs, Corbyn would struggle to achieve the 50 names he needs (though some rebels such as Lisa Nandy have backed him). But a former shadow cabinet minister told me: "There's a majority for JC on the NEC. But one or two may feel they should uphold legal advice. This is going to end up in court either way."

When Eagle was interviewed by Robert Peston this morning, she made her view clear: "He will have to find the nominations". The former shadow first secretary of state was a member of the NEC until her resignation two weeks ago. Eagle was replaced by Corbyn ally Jon Trickett, the new shadow business secretary, but the body could still find against the leader. Jon Ashworth, the shadow minister without portfolio and a Tom Watson ally, avoided resigning from the shadow cabinet in order to retain his NEC seat.

After Watson yesterday ended talks with trade union leaders over Corbyn's position, Unite general secretary Len McCluskey declared: "Should there have to be a leadership election, I must warn that any attempts to keep Jeremy Corbyn, elected just ten months ago with an enormous mandate, off the ballot paper by legal means risks a lasting division in the party". But Corbyn's opponents will argue that they are merely upholding the party's rule book. They will point to the precedent of 1988 when Neil Kinnock was forced to reseek nominations after being challenged by Tony Benn (a rebellion supported by Corbyn). A Labour MP derided Corbyn's stance: "It's all about party democracy but if the NEC don't do so as I say then I'll take legal action against them." Labour's struggle is set to move from parliament to the courts.