The UK government's assertion that "no deal is better than a bad deal" is unsubstantiated without an economic assessment, a report published by the Committee on Exiting the EU on Tuesday (4 April) said.
The parliamentary committee asked the government to provide an economic assessment on the impact of leaving the European Union (EU) without any agreement.
It further argued that there was no evidence that steps were being taken to offset the damaging effect of having such an outcome.
The committee said that a "no deal" between the UK and EU at the end of the negotiating period would see the country fall back on trading under World Trade Organization (WTO) rules.
In the latest report, it has asked the government to explain "what contingency planning is taking place" for the risk that could follow.
The report comes just days after May triggered Article 50, the formal divorce procedure with the EU. While short on detail, she was upbeat about the UK's future during an interview with Andrew Neil after formally launching the Brexit process.
Hilary Benn, the Chair of the Exiting the European Union Committee, said that the UK's deal with the EU would primarily be dependent on the remaining nations in the bloc.
"The UK is about to enter into enormously important and complex negotiations covering trade, customs rules, access to the single market, security and foreign policy co-operation and the rights of UK and EU citizens at home and abroad.
"We all want the best possible deal for the UK but what we are able to secure will ultimately depend on what the 27 Member States are prepared to agree to," he explained.
He asked the UK to be prepared for the worst-possible situation. "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.