Boris Johnson is to assemble his Cabinet for an emergency meeting to discuss the Commons “super Saturday” showdown on his Brexit deal.

Ministers will head to Number 10 at 4pm for an update on the European Council and to “look ahead” to the historic Saturday sitting where the Prime Minister will put his Withdrawal Agreement to the test, Downing Street confirmed.

He is expected to be on the phone all day in attempts to shore up support on his own Government benches, while his team hold one-on-one conversations with Labour MPs and former Tories who were sacked after rebelling on no-deal.

Sir Nicholas Soames – one of the 21 Tories to have the whip withdrawn – gave Number 10 hope when he told Newsnight on Thursday that he would vote in favour of the deal and that his 20 colleagues who had the whip removed would “by and large vote for it”.

Talks are thought to have largely ended between Downing Street and the DUP, following the unionist party’s decision to dig in over their opposition to the divorce terms.

The DUP’s Brexit spokesman, Sammy Wilson, urged Tories to “join us in rejecting this deal”.

Mr Johnson is set for in-person meetings with members of the European Research Group (ERG), the hardline band of Eurosceptic Tory MPs, throughout Friday.

ERG chairman Steve Baker said he would not be commenting further.

Prominent Brexiteer Mark Francois, speaking to reporters before attending a meeting at Downing Street, said he had “concerns” about the deal and that he was “undecided” over whether to give it his support.

MPs are set to meet on a Saturday for the first time in almost 40 years to decide whether to back the PM’s deal.

Sir Oliver Letwin, a former Tory Cabinet minister and now Independent MP, has put forward an amendment that, if accepted and approved, would force the Government to pass the European (Withdrawal Act) Bill (WAB) before a meaningful vote could be held.

Number 10 said it intends to bring WAB forward on Monday, should a majority be found for the meaningful vote.

The amendment is a sign of the distrust that has developed between Downing Street and MPs opposed to no-deal that they want the Brexit deal written into law before the October 31 deadline so there is no room for obfuscation.

Ex-Tory MP Stephen Hammond said Sir Oliver’s amendment was “quite specific”.

“What it says is that Brexit doesn’t happen until all stages of the implementation Bill are passed,” the Independent MP told reporters at Westminster on Friday.

“What it is born out of is the concern that someone might choose to vote for tomorrow’s deal, thereby satisfying the Benn Act, and then choose to do something either by accident or by design which frustrates the implementation Bill and then there is a possibility of us leaving the European Union without a deal.”

It will be up to Commons Speaker John Bercow to decide whether the amendment will be voted on by MPs.

A spokesman for the PM said: “I’m not going to get into amendments that have not been accepted.”

Meanwhile, Jon Lansman, chairman of Momentum, Labour’s left-wing grassroots movement, advocated for sacking any party MPs who get behind Mr Johnson’s agreement with Brussels.

Labour MPs representing Leave seats are known to be seeking legal amendments or further legislation that would protect workers’ right in exchange for their support for the deal.

Ronnie Campbell, Labour MP for Blyth in Northumberland, has already confirmed that he plans to back the divorce proposals and told Radio 4’s World At One that as many as 11 others could join him.

He said he was “happy” with the Tory promises on workers’ rights.

Mr Lansman tweeted: “Johnson’s deal will be a wrecking ball through the lives & well-being of ordinary people across Britain.

“Labour MPs cannot and must not vote for it. If they do, the NEC will have no choice but to replace them with a new, socialist Labour candidate at the next election.”

Shadow chancellor John McDonnell told BBC Radio 4’s Today programme that there would be “consequences”, to be determined by the Opposition chief whip, for those who disobeyed party orders to block the deal.

Asked whether the party would withdraw the whip from rebels, a Labour spokeswoman pointed to Jeremy Corbyn’s earlier comments.

Speaking on Wednesday, Mr Corbyn said: “I believe in the power of persuasion rather than the power of threat.”