Theresa May has told the BBC that MPs will have a choice between her proposed deal with the EU - or no deal at all.
She was also critical of a plan by Brexiteers to resolve the Irish border issue, saying it would create a "hard border 20km inside Ireland".
The prime minister did admit that under "no-deal there would be some short-term disruption".
Shadow Brexit secretary Keir Starmer said no-deal would be "catastrophic" and people were "too casual about it".
He told Panorama: "It's not viable. It's rhetoric, not reality, and it can't be allowed to happen."
But Mrs May said it was the government's job to "make sure we make a success of no-deal, just as we make a success of getting a good deal."
Her comments were in response to questioning about the Bank of England's governor Mark Carney's warning that a no-deal Brexit could see house prices crash by more than a third.
Meanwhile, the International Monetary Fund has said the UK economy will shrink without a Brexit deal.
In its annual assessment of the UK economy, the IMF said that all likely Brexit scenarios would "entail costs", but a disorderly departure could lead to "a significantly worse outcome".
Chancellor Philip Hammond said the government had to listen to the IMF's "clear warnings".
The UK is set to leave the EU on 29 March 2019, and negotiations between the two sides are still taking place.
Mrs May set out her proposals for the key issue of cross-border trade after a Chequers summit in July, but it has been fiercely criticised by some Brexiteers who say plans for a "common rulebook" on goods would compromise the UK's sovereignty.
Speaking to Panorama, Mrs May said that if Parliament does not ratify the Chequers plan "I think that the alternative to that will be having no deal".
BBC political editor Laura Kuenssberg said Theresa May calculated that faced with a "binary choice" of the Chequers deal or no deal, Brexiteers would not have the "chutzpah to say 'no way'" and Remainers would decide that carrying on fighting the plan would be too risky.
But the risks are that the PM cannot say for certain what the final deal will look like - and some Brexiteers were already determined not to vote for it, she added.
Mr Johnson's column in Monday's Daily Telegraph renewed his attack on the Chequers proposals and the government's plans for avoiding new border checks on the Northern Irish border.
He criticised the UK's decision to agree with the EU on the need for a "backstop" to avoid a hard border irrespective of a trade deal, saying the issue was being used "to coerce the UK into becoming a vassal state of Brussels".
Downing Street responded by saying Mr Johnson had been part of the government that signed up to the backstop plan.
In her Panorama interview, Mrs May said there needed to be "friction-free movement of goods" with no customs or regulatory checks between the UK and EU on the island of Ireland, in order to avoid a hard border there.
Last week a group of Brexiteer Tory MPs said a hard border could be avoided by using "established" technology and "modifying" existing arrangements.
Mr Johnson refers to the suggestions by the European Research Group in his column, saying that "extra checks done away from the border" would prevent the need for physical checks when vehicles move between Northern Ireland and the Irish Republic.
But Mrs May insisted that any system of checks was "still a hard border".
"You don't solve the issue of no hard border by having a hard border 20km inside Ireland," she said.
Former Liberal Democrat leader Sir Nick Clegg told BBC Radio 4's Today programme it was an "insult to the intelligence of British voters" for the prime minister to say it was a "choice between either the Chequers fudge or a cataclysmic cliff edge".
Speaking later at a fringe event at the Lib Dem conference in Brighton, Sir Nick claimed European leaders were "seeking to find some way of giving Britain more time" to avoid a no-deal Brexit.
Brexiteer Jacob Rees-Mogg told LBC the prime minister should "try a bit harder" to get a better deal.
Mrs May has found herself embattled with some in her party, after about 50 European Research Group Tory MPs openly discussed how and when they could force her to stand down as prime minister.
On Sunday Brexit-supporting Environment Secretary Michael Gove said the Chequers plan was the right one "for now".
He told the BBC a future prime minister could alter the relationship between the UK and the EU.
Mrs May will attempt to persuade EU leaders of the merits of her plans at a summit in Salzburg on Thursday.
With nearly six months to go until exit from the EU on 29 March 2019, a poll commissioned by BBC Radio 5 Live suggests that the UK remains split over whether Brexit will be positive for the UK.
According to a Comres survey, 50% of British adults feel the overall impact will be negative, whereas 41% think it will be positive.
When asked about the handling of Brexit negotiations, almost 79% of people polled thought that the government had handled them badly, and 63% thought the EU had handled them badly.
The People's Vote campaign, meanwhile, claimed a "fresh wave" of 18-year-olds becoming eligible to vote was "transforming the dynamics of the Brexit debate" because they mostly back staying in the EU.
BBC Panorama, Inside No 10: Deal or No Deal? is on Monday 17 September at 20:30 BST on BBC One as part of a week of in-depth coverage across the BBC to mark Brexit: Six Months to Go.