Theresa May has refused to rule out another Commons vote on her Brexit deal if MPs reject it the first time.
The PM said she thought she could win the vote on 11 December despite dozens of Tory MPs being against the deal.
In an interview with the BBC’s Laura Kuenssberg, she urged MPs to "deliver on the vote of the referendum".
Under Commons rules, the prime minister is not meant to ask MPs the same question twice – she would have to change the contents of her deal.
Alternatively, if enough MPs indicate they have changed their minds after voting the deal down, it could be held again, but it would be up to the Speaker to decide whether to allow that.
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Pressed by Laura Kuenssberg on whether she would attempt to hold another vote, she said: "I’m focused on the vote that is taking place on 11 December and I want everybody who’s going to participate, all members of Parliament, to focus on what this vote does."
Mrs May, who is in Buenos Aires, Argentina, for a G20 summit of world leaders, accused Labour of having no alternative plan.
And by threatening to oppose her deal in the Commons vote, she claims Jeremy Corbyn’s party was effectively advocating leaving without a deal.
But the Labour leadership has said it is ready to support a cross-party amendment to the vote that would explicitly rule out a no-deal. The amendment would not be binding but it would be hard for the PM to ignore it, if it is passed by Parliament.
Leading Tory Brexiteer Jacob Rees-Mogg has, meanwhile, warned in the Daily Telegraph against efforts to "frighten" people into backing what he called "a non-Brexit Brexit",
But European Council President Donald Tusk has stressed that the deal the EU struck with Theresa May was the "only possible one".
He said: "If this deal is rejected in the Commons, we are left with, as was stressed a few weeks ago from Prime Minister May, an alternative – no deal or no Brexit at all.
"I want to reassure you that the EU is prepared for every scenario."
Earlier Mrs May ruled out moving to a Norway-style deal with the EU, an idea being promoted by some Tory MPs. She said this was unacceptable as it would see freedom of movement continue.
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May’s deal versus the alternatives?
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It is widely expected that MPs will reject the EU withdrawal agreement and blueprint for a future trade deal agreed with the EU.
In anticipation of this happening, some MPs are trying to mobilise support for the so-called "Norway Plus" option, which they claim could win support across the House of Commons.
Under their plan, the current withdrawal agreement would be honoured but the UK would seek to rejoin the European Free Trade Association, which it belonged to before entering the European Economic Community in 1973 – on an indefinite basis.
If EFTA’s existing members – Switzerland, Norway, Liechtenstein and Iceland – agreed, it would allow the UK to retain membership of the customs union and full access to the single market.
Advocates of the plan say the UK would still be outside the Common Agricultural Policy and the Common Fisheries Policy – but it would also mean continued free movement of people.
Mrs May said this kind of deal would not fulfil the referendum pledge to take back control of the UK’s borders, laws and money.
But three former Labour foreign secretaries have warned of the damage to British influence around the world if the UK leaves the EU.
David Miliband, Jack Straw and Margaret Beckett told the Financial Times they all backed the People’s Vote campaign for another referendum.
Mr Straw told the BBC he believed there was a "huge appetite" among the public to have their say again.
"At the moment, people are having to go sullenly to accept the situation is as it is – not remotely anticipated by the Brexiteers nor anything like that which was promised," he told Radio 4’s Today.
Ministers step up efforts to sell deal
In a speech in Bristol, International Trade Secretary Liam Fox argued that while the deal will not please everyone, critics "are yet to face up to" the "tough choices" she had to make.
Mr Fox told the BBC that the PM was "changing the public mood" and while there were alternatives to her deal which would give the UK a freer hand to strike other trade deals, that could come with a "price" in terms of reduced access to EU markets.
The Financial Times says Mrs May is enlisting the support of senior Brexiteers such as Michael Gove and Geoffrey Cox to try and sell her controversial Irish "backstop" plan to sceptical Tory MPs.
Mr Fox said he was not "enthusiastic" about the backstop, which could see the UK enter a customs partnership with the EU until its future relationship is sorted out and without the unilateral right to pull out.
But he insisted the chance of the backstop, described as an "insurance policy" by Mrs May, actually coming into force was slight as it was just as "unpalatable" to other EU members, including the Republic of Ireland.
And Treasury minister Liz Truss, who is backing Mrs May to get the agreement through Parliament, suggested parts of it could be renegotiated after the UK left the EU.
"Some things are set in treaties but no parliament can bind its successor."