Mark Francois declared yesterday that the European Research Group will vote against Chequers. In one sense, of course, it will do no such thing. There won’t be a vote on a proposal called Chequers in the event of a Brexit deal – or on one called Canada, Canada Plus Plus Plus, SuperCanada, SuperChequers, Norway, and so on.

Rather, there will be a vote on a Withdrawal Agreement and a political declaration. If the last is too specific, Theresa May risks Conservative MPs – and not necessarily just the harder Brexiteers – picking holes in it and helping to vote it down. But if it is too vague, she risks ERG members and other Tory MPs asking why we should hand £40 billion or so to the EU, under the terms of part of the Withdrawal Agreement settled last December, in exchange for…nothing very clear at all. In which case they will also vote it down with other MPs, or try to.

Any declaration will none the less have to be based on something, and the significance of Francois’ intervention is that the ERG is, for the first time, formally committed to oppose one if it is based on Chequers. The ERG is making much of this: ConservativeHome is told that the announcement was “official and significant”. The choice of MP to make it was significant. Unlike, say, the star of our Moggcast, Francois is a privy councillor, has been a Minister, and was a senior one at that – Minister of State for the Armed Forces.

Perhaps more to the point, he was also a whip in the early years of the Coalition, serving in one of the top four posts in the office. “He was chosen specifically to send a signal from one of life’s natural whips to the current ones,” we are told. Certainly, Francois will know the numbers and the drill. He said that “well north of 50” Tory MPs will vote against anything based on Chequers. We treat that figure with healthy scepticism.

But there can be little doubt that enough would do so to make the passage through the Commons of any proposal based on Chequers very difficult indeed, if all Opposition MPs combined to oppose it too. The plan looks to be on its last legs. In Cabinet, it isn’t just the Brexiteers who are casting about for an alternative: former Remainers such as Sajid Javid, Jeremy Hunt and Liz Truss are sympathetic to a Canada-type plan. The ERG move is designed to kill Chequers off altogether.

Our sense is that the plan will survive next week’s Conservative Party conference, but probably not much longer. As we said yesterday, Cabinet members don’t want to weaken the Prime Minister as she prepares for Birmingham. Her reiteration yesterday of the Government’s commitment to cut corporation tax further is an early sign of how she will use her bully pulpit to fight back next week.