Reality Check: Could Labour rebels become the opposition?

The claim: MPs who do not support Jeremy Corbyn's leadership could go to the Speaker and ask him to recognise one of them as the leader of the opposition.

Reality Check verdict: The rules are ambiguous enough for the decision to be left to the Speaker. He could rule that the wishes of the majority of Labour MPs outweighed the rules of their own party, but he could also rule the other way and decide that if they wanted to be the official opposition they had to break away and form a new party.

Newsnight political editor Nick Watt revealed on Monday that groups of Labour MPs, both opposing and supporting Jeremy Corbyn's leadership, had been discussing with parliamentary officials whether the rules would allow a breakaway group of a majority of Labour MPs to ask the Speaker to recognise one of them as the leader of the opposition.

If Mr Corbyn wins the current leadership election, Nick Watt thought it unlikely that there would be a full split in the party, as happened with Ramsey Macdonald in 1931 and the SDP in 1981.

But would parliamentary rules allow for someone other than the elected Labour leader to be considered as the leader of the opposition if he or she had the support of enough MPs?

The Ministerial and Other Salaries Act 1975 defines the leader of the opposition as: "being the Leader in that House of the party in opposition to Her Majesty's Government having the greatest numerical strength in the House of Commons".

It also adds that if there is any doubt about this then "the question shall be decided for the purposes of this Act by the Speaker of the House of Commons".

Gavin Freeguard, from the Institute for Government, told the BBC he thought a large enough group from the Parliamentary Labour Party could indeed break away and name a different leader of the opposition.

But the Labour Party rule book is clear that the leader of the Labour Party and the leader of the Parliamentary Labour Party must be the same person.

Nigel Fletcher, director of the Centre for Opposition Studies, said that the 1975 act suggested: "Labour MPs could elect a new leader who would be entitled to the official position."

"However, the Labour Party constitution is equally clear that its elected leader is automatically leader of the parliamentary party. The law states where there is doubt it is for the Speaker to decide, and there are reports he has indicated MPs would have to form a new party if they wanted to depose Mr Corbyn whilst he remains leader of the party in the country."

Meg Russell, director of the UCL Constitution Unit said: "If a large, breakaway group of Labour MPs wanted to go to the Speaker and claim to be the opposition without breaking away officially from the Labour Party, that could place the Speaker in quite a difficult position. In effect, he'd be making a judgment as whether the Labour Party continued in its current form."