Senior Tory Remainers and Leavers urge rebels to back Theresa May on EU vote or risk toppling the government

MPs are gearing up for a fraught two-day contest over the EU (Withdrawal) Bill

Conservative Brexit factions have united to order party rebels to back Theresa May's flagship Brexit bill or risk toppling the government.

Ex-home secretary Amber Rudd, a leading Remain supporter, and Eurosceptic former party leader, Iain Duncan Smith, formed an unlikely alliance to urge party colleagues to back the prime minister in a series of crunch votes in parliament this week.

MPs are gearing up for a fraught two-day contest over the EU (Withdrawal) Bill, where the government is trying to overturn all but one of the 15 Lords amendments on issues ranging from customs to a meaningful vote for parliament on the final Brexit deal.

With a knife-edge result expected, Tory whips will be ramping up the pressure on potential pro-EU rebels to ensure they have the numbers to win.

In a joint article in The Sunday Telegraph, Ms Rudd and Mr Duncan Smith said the vote was "not about competing visions of the future but about ensuring legal certainty at our point of departure".

"Jeremy Corbyn will do everything he can to stop us.

"That includes cynically trying to frustrate the Brexit process for his own political ends, as he will try to do next week when the Commons votes again on the EU (Withdrawal) Bill.

"So it behoves us all to demonstrate discipline and unity of purpose in support of the Prime Minister.

"We cannot allow ourselves to become divided."

The prime minister has tried to win over Tory rebels by offering a 28-day breathing space if parliament votes down her Brexit deal, but rejected other concessions won in the House of Lords over keeping Britain in the customs union and the single market.

While ministers are confident of winning most of the votes, pro-EU Tory rebels believe they could be vulnerable over the key measures on customs and the meaningful vote.

It would only take a handful of Tories to rebel for Ms May to lose key votes, although the Conservatives will be backed by the DUP and also may have support of several pro-Brexit Labour MPs.

Former deputy prime minister, Damian Green, wrote in the Sunday Express that most of the crucial votes would "pass easily".

He said: "The Westminster air is again full of the scent of rebellions, chaos and catastrophic Government defeats.

"I predict they simply won't materialise for one simple reason: the whips can count.

"If they think that the Government won't have a majority, they advise a change in policy."

Prominent Brexiteer Jacob Rees-Mogg urged colleagues to get behind the bill even if it "goes against some of their most deeply held political beliefs".

He told The Sun: "Ultimately, this bill is not the future of relationship with Europe. It is a technical one, making UK law work once we leave.

"But the Lords has used it as a Christmas tree to add its favourite EU baubles too."

Ms May, in Quebec for the G7 summit, denounced peers for amending the bill, which she said exceeded their role as a revising chamber.

"Let's remember what the Withdrawal Bill is for: it's about delivering a statute book that is ready for Brexit day," she said.

"Of course, the Lords has a revising role to play - but some of the amendments that were passed and the comments that were made went far beyond that.

"You had peers talking about stopping Brexit or trying to tie the government's hands in the negotiations."