Keir Starmer’s announcement that Labour will vote against whatever Brexit deal Theresa May brings before parliament has confirmed what many in Westminster had long assumed. This afternoon, Jacob Rees-Mogg’s European Research Group did the same.

Asked how the 80-strong group of hard Brexiteers would vote on the final deal on Radio 4’s The World at One this afternoon, ERG officer Mark Francois said the group wanted the Prime Minister to drop her Chequers plan – and added that they would join Labour in voting against the final Brexit deal if she did not.

“If push really comes to shove, and they try to put Chequers through the House of Commons, then I and my colleagues will vote against it,” he said. “Myself and my colleagues in the ERG cannot vote for Chequers.”

His words are an ex cathedra statement of intent by the ERG leadership and is significant, both in its timing and delivery. It compounds the blow inflicted by Starmer this morning and confirms that the Prime Minister has no majority for her current plans (despite this, she has signalled to her cabinet that she will dig in).

An ERG source says Francois, a well-liked former whip, was deliberately chosen to deliver the message with “deliberate, fraternal menace” in a bid to underline the “factional and organisational imperative” for the government to change course to a Canada-style deal of the sort unveiled by David Davis and Boris Johnson yesterday. The ERG believes there is a majority for such a deal in the Commons. “Everyone likes Canada,” a source says.

The problem for Downing Street is that any move in that direction risks alienating the more hardline of the Tory remainers, and could nuke any lingering hope they have of encouraging some Labour MPs – beyond its Leavers – to vote with the government come what may. Then there is the question of the Irish border. Is also unclear, to put it mildly, how the government could pursue such a policy without violating either its own red line on maintaining the constitutional integrity of the UK or its commitment to avoiding a hard border on the island of Ireland.

But those questions are secondary to the one facing the Prime Minister: can she pass any Brexit deal in the Commons? On today’s evidence, it will be near impossible to answer in the affirmative.