Theresa May on Monday embarks on a two-week campaign to sell the historic Brexit deal agreed by European leaders, telling MPs that if they reject it, they risk plunging the country into “more division and uncertainty”.

The deal, approved in Brussels on Sunday, aims to deliver a smooth divorce to end Britain’s 45-year involvement in the European project, although many details of the future relationship between the two sides have yet to be agreed.

Mrs May will tell MPs that if they reject the deal agreed in Brussels, it would take talks “back to square one”. She will add: “It would open the door to more division and more uncertainty, with all the risks that will entail.”

The prime minister will also rally her cabinet in support of the deal, amid concerns in Downing Street that some Eurosceptic ministers — including environment secretary Michael Gove or transport secretary Chris Grayling — have not been publicly selling the plan.

Steve Barclay, the new Eurosceptic Brexit secretary, suggested that some of his colleagues needed to get off the fence.

“It’s up to all of us in the cabinet to make the case to our colleagues,” Mr Barclay told the BBC’s Today programme on Monday morning. He said that the Commons vote, pencilled in for December 12, would be “challenging”.

Mr Barclay also downplayed warnings from French president Emmanuel Macron that Britain’s future relationship with the EU would be tied to beneficial access for EU fishermen to British waters.

“We have not agreed to any linkage between access to waters and access to fish,” he said.

Meanwhile some members of Mrs May’s cabinet are canvassing support for Plan B scenarios, should the prime minister fail to win backing for her deal in a Commons voted scheduled for December 12.

Mr Gove and Amber Rudd, the pro-EU work and pensions secretary, have argued that a “Norway-style” model could be taken off the shelf in the event of a stand-off at Westminster.

Both have floated the idea that Britain could temporarily stay in the European Economic Area, giving Britain access to the single market, pending the negotiation of a looser Canada-style free trade agreement with the EU.

But such a plan would be even less acceptable to many Eurosceptics than Mrs May’s deal, since it would imply free movement, payments for EU projects and rule-taking from Brussels. Some MPs would fear the “temporary” plan could become permanent.

Meanwhile Andrea Leadsom, the Eurosceptic leader of the House of Commons, is exploring ways to “manage” a no-deal exit, agreeing side deals with the EU to limit the potential chaos if Britain left the EU without any deal at all.

Britain is scheduled to leave the EU on March 29 2019 under the Article 50 process, but Ms Rudd is among the ministers who would oppose such an exit.

Although the departure date is set down in law, Keir Starmer, shadow Brexit secretary, said parliament would find a way to stop a no-deal exit. Philip Hammond, chancellor, has said such as scenario would result in “economic chaos”.

Meanwhile, Mr Barclay said “a decision will be made in due course” on whether Mrs May would take part in a television debate to sell her deal.

Jeremy Corbyn, Labour leader, indicated he would “relish” the prospect of taking part in such a debate. In the 2017 general election the prime minister refused to participate in any debates.

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