The Brexit negotiations aren’t between 650 MPs but between the United Kingdom and the 27 other EU nations. Emmanuel Macron has given the British parliament a reminder of this by telling journalists that he will veto any extension of Article 50 unless there is a “new choice” by the United Kingdom to justify the decision.

Elsewhere, Pedro Sanchez, the Spanish prime minister, has confirmed what we already know: he will use his right of veto to extract further concessions on the question of Gibraltar.

Does that create enough uncertainty about whether an extension will be agreed upon for a critical mass of Labour MPs to decide they’d better back May’s deal on 12 March? The Prime Minister certainly hopes so, and is set to unveil further concessions on workplace rights in a bid to sweeten the deal.

Yet after 20 Brexit ultras voted against the government last night we have a sense of the size of the European Research Group’s hard core, the bit that would still vote against the deal even if the attorney general, Geoffrey Cox, returns with sufficient assurances on the backstop to win back the DUP and the majority of the ERG.

It’s not written in stone that it will be those 20 who hold out. But just as the 15 Labour MPs to rebel against the whip on the EEA don’t always vote against measures to soften Brexit, but the number of Labour rebels is always at least 15, we can safely put the number of Brexit ultras around the 20-MP mark.

You can see the problem here: May’s hope is that if she gets a legal assurance on the backstop she can get most of the ERG back on board and therefore pass the deal with the support of Labour’s committed Brexiteers and its MPs who want to back a Brexit deal for one reason or another. But 20 is, obviously, a bigger number than 15.

However you slice it, there aren’t enough Labour MPs in the group May is targeting to compensate for the Conservative MPs she is certain to lose.

It’s why, if May can’t create a forced choice between her deal and the cliff-edge, and if the People’s Vote campaign can’t achieve a transformation in the attitudes of MPs towards another vote, the only paths out are either a very different type of Brexit to the one on offer or an early election, which may simply return a parliament even more incapable of negotiating Brexit than this one.