There is growing concern that Theresa May's Brexit deal will be voted down by MPs in December, even if it is approved by her Cabinet this week. 

At the centre of concerns remains proposals on how to keep open the border between Northern Ireland and the Republic of Ireland.

Parliamentary defeat would be disastrous for May. It would increase the chance of a no-deal Brexit and strike a catastrophic blow to her authority.

Theresa May's Brexit deal is being declared dead before it has even been born.

The British prime minister is set for a crunch meeting with her Cabinet early this week, where she will attempt to get her EU withdrawal agreement signed off by senior ministers.

But even if she does get approval from her top team, there is growing concern that the Brexit deal will be voted down when it is put before MPs in December, according to a number of reports this weekend.

Defeat in Parliament would be disastrous for May. It would significantly increase the chance of a no-deal Brexit and strike a catastrophic blow to her authority, likely provoking a leadership challenge.

At the centre of concerns remains proposals on how to keep open the border between Northern Ireland and the Republic of Ireland. There are fears that the so-called backstop agreement on the Irish border could make Britain a vassal state of the EU and increase the possibility of a border between Northern Ireland and the rest of the UK.

Transport Minister Jo Johnson resigned on Friday, voicing fears held by both Brexiteers and those who wish to remain in the EU. "To present the nation with a choice between two deeply unattractive outcomes, vassalage and chaos, is a failure of British statecraft on a scale unseen since the Suez crisis," he said.

ITV Political Editor Robert Peston wrote on Saturday that May's Brexit deal "looks dead even before it's born." He said that without the support of Labour, May will lose a meaningful vote in Parliament.

"The destination is constitutional crisis, where legislature will be in irreconcilable conflict with executive, Commons at odds with PM and her cabinet," Peston said in a post on Facebook.

This was supported by a report in The Sunday Telegraph, which said May's agreement will be blocked by MPs even if she secures Cabinet approval. "She could force it through [Cabinet] with a majority, but she wouldn't get it through the Commons," one minister told the newspaper.

Former Brexit minister Steve Baker and the DUP's Brexit spokesman Sammy Wilson, took the unusual step of joining forces to pen an open letter to May in The Sunday Telegraph. They said they would vote against her deal unless an alternative solution is found.

"We share the Prime Minister’s ambition for an EU free trade agreement, but not at any price, and certainly not at the price of our union," they said. "If the government makes the historic mistake of prioritising placating the EU over establishing an independent and whole UK, then, regrettably, we must vote against the deal."

Peston, The Sunday Telegraph, and The Sunday Times all reported that there are likely to be more ministerial resignations. The Sunday Times said four Remain-leaning ministers were on the brink of quitting, while the Telegraph said politicians would fall like "paper tigers."