Liam Fox has rubbished Boris Johnson’s claim that Britain could use world trade rules to continue tariff-free trade with the European Union in the event of a no-deal Brexit.
The international trade secretary said free trade would require the backing of the EU, and they have no plans to support such a move.
“A 'no deal' scenario, by definition, suggests that there would be no mutual agreement between the UK and the EU on any temporary or permanent arrangement,” he said.
“The European Union has made it clear on a number of occasions that full tariffs will be applied to the United Kingdom in the event of 'no-deal'.”
Mr Johnson has argued a provision under the general agreement on tariffs and trade, known as Article 24, would be used to avoid tariffs for up to 10 years.
He told talkRADIO’s political editor Ross Kempsell “plan B” is to leave on an Article 24 agreement.
However Mr Fox, who is backing Jeremy Hunt in the leadership contest, said Article 24 was not enough to guarantee free trade after a no-deal Brexit.
“Article 24 would not, by itself, allow the UK to maintain tariff-free trade with the EU in the absence of a negotiated agreement,” he said.
“It is important that public debate on this topic is conducted on the basis of fact rather than supposition, so that we are able to make decisions in the best interests of our country.”
Mr Johnson has also been criticised by former civil service chief Lord Kerslake for his pledge to leave the EU on October 31 "come what may".
Mr Kerslake said: "It is always a good maxim in politics not to enter a room unless you know that you can get out of it."
"Boris Johnson has not only entered the room but he has put on the straitjacket, padlocked the door and started the tap running."