No assessment of the economic implications of leaving the EU without a trade deal has been undertaken by the Government since last year's referendum, Brexit Secretary David Davis has said.
Mr Davis confirmed that leaving under World Trade Organisation rules would mean tariffs of 30-40% on agricultural exports and 10% on cars, the loss of EHIC health insurance cards for travellers and passporting rights for financial sector firms, as well as departure from the EU-US Open Skies arrangements for air transport.
But he said it will be possible to devise mitigating action in response to these issues, and it would be "otiose" to estimate their economic impact until that work has been done.
He told the House of Commons Exiting the EU Committee that he expected to be able to provide forecasts in about a year's time.
His comments came as the European Council president Donald Tusk said that Europe will not be "intimidated" by British threats to walk away from trade talks if it cannot get a good deal.
In a statement to the European Parliament, Mr Tusk dismissed suggestions that a failure to reach agreement in Brexit talks would be worse for the EU than for Britain, telling MEPs: "A 'no-deal scenario' would be bad for everyone, but above all for the UK."
Mr Davis has briefed Cabinet colleagues to be ready for the "unlikely scenario" of the UK crashing out of the EU without a deal - a prospect which Foreign Secretary Boris Johnson said this weekend would be "perfectly OK".
Prime Minister Theresa May has made clear that she regards no deal with the EU as being better than a bad deal.
Asked whether he thought leaving without a deal would be bad for the UK, Mr Davis told the committee: "I think it is not as good an outcome as a free trade, friction-free, open agreement, which is why we are trying for that."
Confirming that no assessments of the economic impact of failure to reach a deal had been carried out since his appointment as Brexit Secretary, Mr Davis told the committee's chair Hilary Benn: "Any forecast you make depends on the mitigation you make, and therefore it would be rather otiose to do that forecast before we have concluded what mitigation is possible."
But he added: "You haven't asked me about the upsides - for roughly 60% of our trade we could relax things the other way."
Explaining Mrs May's "no deal is better than a bad deal" mantra, Mr Davis said: "She said that because in the emotional aftermath of the referendum, there were lots of threats of punishment deals and all the rest of it.
"We had to be clear that we could actually manage this in such a way as to be better than a bad deal, and that is true.
"I can't quantify it for you yet. I may well be able to do so in a year's time. It's not as frightening as some people think, but it's not as simple as some people think."
Mr Davis took a swipe at Mr Johnson's TV interview comments, telling the committee: "I do my job on the basis of facts and data and research and analysis and operational planning, and off the back of that I will give answers that are accurate and factual - not throwaway lines in interviews, factual answers."
Mr Benn responded: "Perhaps you should do all the interviews on this, rather than some of your colleagues."
The Brexit Secretary said he expected royal assent to be granted on Thursday to the Bill giving Mrs May the power to start withdrawal negotiations.
But he declined to discuss the contents of the letter informing the European Council of Britain's intention to withdraw, which the Prime Minister is due to send to Brussels by the end of March.
He denied that the Government had postponed a plan to issue the letter on Tuesday this week, saying this would not have been possible because of the timing of royal assent.