The Prime Minister's claim that "no deal is better than a bad deal" has been criticised as unsubstantiated by a parliamentary committee.
MPs of the cross-party Brexit Committee have warned Theresa May's claim that "no deal is better than a bad deal" was "unsubstantiated" until an assessment of the economic consequences was published.
However, the pro-Brexit MPs who are part of the committee have refused to back the report, saying it is too pessimistic.
Five Conservatives, including former ministers John Whittingdale and Dominic Raab, and Democratic Unionist Sammy Wilson voted against the report, but were outnumbered by 10 Labour, Conservative, Liberal Democrat, SNP and SDLP members, who all backed staying in the European Union.
The report assesses the government's objectives for the negotiations to come as May oversees Britain's departure from the European Union.
The Prime Minister triggered Article 50 last week, kicking off the process of withdrawing Britain from the EU. The government had set out 12 principles, including migration control and "taking control" of Britain's own laws.
The Brexit Committee's report said without an assessment of "no deal" having been done and without evidence that steps are being taken to mitigate what would be "the damaging effect" of such an outcome, the government's assertion that no deal would be better than a bad deal, was unsubstantiated.
Hilary Benn MP, chair of the Exiting the European Union Committee, said: "The government is right to try and negotiate both the divorce settlement and a new trading relationship in tandem, but it should also be prepared for the worst case – i.e. that a new trade agreement is not reached or ratified by the day we leave – because the timescale allowed by Article 50 is particularly tight.
He added that while everyone wants "the best possible deal" for the UK, what will be secured "will ultimately depend on what the 27 member states are prepared to agree to".
Benn said the government needed to conduct a thorough assessment of the economic, legal and other implications of leaving the EU without a deal in place.
The MPs also said it was essential for parliament to get a vote on whether to proceed if no deal was reached.
Brexit secretary David Davis said the government was clear no deal "is not what we want or expect", but that it would be better "than a deal which sought to punish the UK".