Theresa May has urged MPs to think about their constituents, rather than reject her deal for leaving the EU.
The PM, who was on her way to the G20 summit in Argentina, said her plan would protect the “jobs and livelihoods and security” of their constituents.
Mrs May urged MPs to concentrate on the deal she had negotiated with the EU.
And she accused Labour of advocating leaving without a deal by rejecting her Brexit compromise while not putting forward a “proper alternative”.
Labour argues a better agreement could still be negotiated with Brussels.
Writing in the Daily Telegraph, leading Brexiteer Jacob Rees-Mogg has warned against efforts to “frighten” people into backing what he called “a non-Brexit Brexit”.
Mrs May has been trying to gather support for the withdrawal agreement she has negotiated with the EU, ahead of a Commons vote on 11 December – but it is widely expected that MPs will reject it.
Speaking to reporters on her flight to Buenos Aires, Mrs May insisted she had not given up hope of winning the vote, but said if MPs failed to back her it would mean “division and uncertainty” for Britain.
“Let’s focus on the deal that we have negotiated with the EU, a deal which is good for the UK and good for their constituents,” she said.
Mrs May said people she had met outside Westminster in the last few days had given her an “overwhelming” sense that they wanted MPs to back her deal.
She also rejected the idea of moving to a Norway-style deal with the EU – an idea that has been discussed privately by many MPs – saying such a deal would not end freedom of movement.
Analysis: No clues over possible ‘Plan B’
By Laura Kuenssberg, BBC political editor
However many ways the question was put to Theresa May during a 20-minute press huddle on board the government’s Voyager plane, she was resolutely and determinedly not going to let much slip.
What will she do if she can’t get her vote through? Is there a plan B? Could there be a Norway-style relationship with the EU? Could there be another referendum?
Westminster’s awash with speculation and gossip about what might happen next if her Brexit compromise is killed off by her colleagues.
What is happening with Brexit right now?
Mrs May is due to join US President Donald Trump, China’s President Xi Jinping and Japan’s Shinzo Abe as well as European Council President Donald Tusk and European Commission chief Jean-Claude Juncker at the two-day summit of the G20 group of leading economies.
She is expected to tell world leaders her Brexit deal negotiated with the EU will be good for the global economy.
Mrs May will highlight her plans to strike a free trade agreement with the EU.
But she will add: “For the first time in more than four decades, the UK will have an independent trade policy.
“We will play a full and active role on trade on the global stage, working with friends new and old, at a time of unprecedented global inter-connectedness.”
The summit comes after President Trump suggested that the negotiated deal could threaten any future US-UK trade deal.
What else is the prime minister doing at the G20 summit?
Mrs May is the first serving UK prime minister to visit the Argentine capital, and the second to travel to the country, after Tony Blair in 2001.
The Falkland Islands – still claimed by Argentina, 36 years after the 1982 war with Britain – is likely to be discussed when Mrs May has a meeting with the country’s president, Mauricio Macri.
However, the main focus of their talks will be trade.
Mrs May said: “I am clear that our position on the sovereignty of the Falklands has not changed. What has changed in recent months is we have seen better relations with Argentina.”
What is the G20?
The Group of 20 brings together leaders of 19 of the world’s most industrialised nations – plus the EU making up a 20th member.
Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, Mexico, Russia, Saudi Arabia, South Africa, South Korea, Turkey, the UK and the US are all represented.
What are they talking about at the summit?
The focus of the two-day summit opening on Friday is “fair and sustainable development”, according to the event’s website.
But the gathering has come amid new tension with Russia over Ukraine and a US trade row with China.
US President Donald Trump has cancelled a meeting with his Russian counterpart, Vladimir Putin, in protest at Russia’s seizure of Ukrainian naval boats.
And hopes of progress over tariffs in Mr Trump’s expected talks with Chinese leader Xi Jinping have been dampened.
The summit is also a diplomatic test for Saudi Crown Prince Mohammed bin Salman amid continuing questions about the Saudi state’s possible involvement in the murder last month of journalist Jamal Khashoggi in Turkey.
What is happening in the UK?
In the UK, International Trade Secretary Liam Fox is to defend Mrs May’s deal, saying that while it will not please everyone, critics “are yet to face up to” the “tough choices” she had to make.
In a speech at the Portbury Royal Docks, near Bristol, Mr Fox, who campaigned for Brexit, will also play down reports suggesting that UK economic growth after Brexit would be slower than if the UK stayed in the EU.
In his Daily Telegraph article, Mr Rees-Mogg says a “crisis in trust” in British institutions has been made worse by Brexit.
Referring to the downbeat economic scenarios issued by the Bank of England on the impact of leaving the EU, he said its governor, Mark Carney “warns constantly about Brexit” and was in danger of ruining its credibility.