The prime minister was trying to play down warnings made by chancellor Philip Hammond last week of the major economic consequences of the UK leaving the EU without an exit deal.
Mrs May conceded that no agreement with the EU “would not be a walk in the park”.
She said her government is putting in place measures to ensure it can “make a success of no deal” but remains confident a “good deal” is still a possibility.
Mrs May said Mr Hammond was highlighting “work in progress” figures released in January when he published a letter just hours after the government started revealing its no-deal Brexit preparations.
The chancellor was accused by Tory backbenchers of launching another “project fear” by referring to disputed provisional analysis which claimed GDP could fall and borrowing could be around £80 billion a year higher by 2033/34 if Britain resorted to World Trade Organisation terms.
Mr Hammond said such an impact on GDP would have “large fiscal consequences”. He also said this analysis was undergoing a “process of refinement” ahead of a parliamentary vote on any deal.
Mrs May, asked about the timing and content of Mr Hammond’s intervention, said she had previously labelled the data as a work in progress.
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Speaking to reporters on her trade mission to Africa, Mrs May referred to comments made by World Trade Organisation director general Roberto Azevedo.
“He said about a no deal situation that it would not be a walk in the park but it wouldn’t be the end of the world,” she said.
“What the government is doing is putting in place the preparations such that if we’re in that situation we can make a success of it, just as we will make a success of the good deal I believe we’re able to get and the good deal we’re working to get.”
Mrs May was also challenged on whether she would order her MPs to vote for no deal if her preferred approach – agreed following talks at Chequers – was not secured with the EU.
She replied: “I’ve said right from the beginning that no deal is better than a bad deal.
“I think it’s absolutely right that the government is putting the preparations in place for no deal because we don’t know what the outcome of this is going to be.
“But alongside that what we’re doing is working for a good deal.
“I believe what we’ve set out in the Chequers arrangement, set out in the white paper is a deal that benefits not just the United Kingdom but benefits the European Union as well.”
Eurosceptic Tories have criticised the government’s proposals, which include a “common rulebook” with the EU on goods, amid fears it could restrict the UK’s ability to do external trade deals outside of Europe.
Mrs May also said the UK was working to secure a deal by October and within a timetable which meant Brexit could occur in March 2019.
On whether Tory MPs face a backlash from their local party associations for supporting a second EU referendum, Mrs May added: “I believe that what matters to local associations is what the Conservative government is delivering for them – and what we’re delivering is what the people voted for.”
Mrs May also reiterated the UK government’s desire to end free movement is “non-negotiable”.