Jeremy Corbyn leaves after addressing a gathering of supporters demonstrating in Parliament Square today. REUTERS/Toby Melville Jeremy Corbyn hinted yesterday — perhaps inadvertently, perhaps he merely misspoke — that he is willing to split the Labour party into two new organisations in order to win his struggle against the MPs who want him out. MP Owen Smith yesterday asked Corbyn if that is what he was doing, according to the Financial Times:

Mr Smith, according to those present, asked Mr Corbyn: “Are you prepared to split the party over this?” The Labour leader said he did not want to but added: “But if necessary ...”

To those present, it was a shocking admission. Soon afterwards, Mr Smith and Ms Nandy resigned [their shadow cabinet posts].

"But if necessary"?

What might that mean?

Corbyn is pushing the Labour party into an astonishing internal crisis. Today he lost a "no confidence" vote of his fellow MPs, with 80% of them urging him to step down (172-40). He refuses to, claiming the vote is not within the party rulebook. Corbyn's logic is that the vast majority of Labour's ordinary party members elected him as their leader just months ago, and he represents them, with their mandate. The MPs claim that there is no way he can win the next general election and thus must make way for someone who can broaden Labour's appeal.

At any other time in Labour's history, Corbyn would be toast. But due to the rule change, which let ordinary members vote, he remains the leader of the party.

The frustration of MPs is palpable. Conservative Prime Minister David Cameron has just lost a colossal gamble in the EU Referendum that will remove the UK from Europe, and may break the entire UK into separate pieces. Due to Cameron's resignation, the UK may get a general election later this year. That vote could not be more crucial — if Labour and the SNP can put together a majority on a clear platform of remaining in the EU they could make a case to negate the Brexit referendum and save Britain from economic ruin.

Under any other circumstance, Labour would be in with a fighting chance of winning that vote.

But not with Corbyn at the helm.

Why is Corbyn so stubborn? Why doesn't he make way, when any other MP would have been embarrassed at losing the support of his entire parliamentary party? (For comparison, Margaret Thatcher resigned after winning a leadership vote by 204 to 152.)

One tantalising answer may be that Corbyn believes that the 250,000 votes he received from party members plus the 60,000 members of Momentum, the left-wing group that supported him, are the "real" Labour party, not the Labour MPs elected by the votes of ordinary people. In that scenario, Corbyn is essentially trying to create a new Labour party to the left of the parliamentary party.

The problem is that the actual Labour party is still run in large part by the MPs, their staff, and supporters. They are now bitterly opposed to Corbyn, who has plunged them into civil war at the very moment the Tories look their weakest.

One obvious solution is for either Corbyn or the MPs to leave Labour, or to force the other side to leave, and create a new party. Corbyn already has a proto-party behind him, Momentum, which consists of both Labour members and leftists outside Labour. If that were to happen it is not clear who would retain control of the official party and — crucially — its ability to select MP candidates on the official "Labour" slate. Momentum leader Jon Lansman signaled before the vote that he favours mandatory "reselection" of sitting MPs prior to any new general election, a policy that might give power to the 250,000 new Labour members who voted for Corbyn.

The fear among moderates is that this is the endgame and that Momentum isn't merely a Corbyn fanclub but an "entryist" organisation, a party-within-a-party that is loyal to itself not Labour.

We'll find out the answer to all this just as soon as we find out what "But if necessary" really means.