THERESA May could put her Brexit deal back to the Commons tomorrow. After the Prime Minister told Tory MPs she was ready to quit Downing Street ahead of the next phase of negotiations with Europe, a flurry of prominent Brexiteers, including Boris Johnson, indicated that they would now back her withdrawal agreement.

However, even with those switchers, it’s not entirely clear if the beleaguered party chief will have the numbers to get it through the Commons, as the DUP, whose 10 MPs prop up her minority government, insisted they would still oppose any deal containing the backstop.

And before May can even try to put the deal in front of MPs again, she’ll have to get it past Speaker John Bercow.

Yesterday, he caught Number 10 off guard, again, when he repeated his warning that meaningful vote three, or MV3 as it’s known, could not be brought back to the Commons, unless there had been some fundamental change.

The DUP’s statement came some four hours after May’s announcement.

The Northern Irish Unionists said that while they had had “good discussions in recent days” with the government and that “some progress on domestic legislation has been made,” it wasn’t enough.

They added: “We want to secure the United Kingdom’s departure from, and our future relationship with, the European Union on terms that accord with our key objectives to ensure the integrity of the United Kingdom.

“In our view the current withdrawal agreement does not do so and the backstop, which we warned this government against from its first inception, poses an unacceptable threat to the integrity of the United Kingdom and will inevitably limit the United Kingdom’s ability to negotiate on the type of future relationship with the EU.”

After one journalist speculated that the DUP might abstain, the party’s deputy leader, Nigel Dodds, made clear that would not happen.

“The DUP do not abstain on the Union,” he tweeted.

The European Research Group of Brexit supporting Tory backbench MPs are split on what to do. In a column for the Daily Mail, ERG chairman Jacob Rees-Mogg said he would be guided by the DUP as “guardians of the Union of the United Kingdom”.

Johnson, who attended a meeting of the ERG last night, left without making a comment.

Previously, he has claimed May’s deal wrapped a “suicide vest” around the British constitution.

Former Brexit minister Steve Baker told the meeting he was in a “ferocious rage” after the “pantomime” of May’s announcement and indicated he “may yet resign the whip than be part of this”, a source said.

Nevertheless, Tory MPs have been told to be in the Commons tomorrow.

In the Commons last week, Bercow insisted that “a proposition which is the same or substantially the same may not be brought forward again during the same parliamentary session”.

Yesterday, he said the government had “accepted this constraint”. He added:

“I understand the Government may be thinking of bringing ‘meaningful vote three’ before the House either tomorrow or even on Friday if the House opts to sit that day.

“Therefore in order that there should be no misunderstanding, I wish to make clear that I do expect the Government to meet the test of change.”

A Downing Street spokesman said: “It’s clearly for the Speaker to determine the test he’s set for himself. What the PM is determined to do is to secure the votes in order to allow us to pass the meaningful vote and leave the EU as quickly as possible.”