David Davis has been ridiculed for suggesting the UK could enter a post-Brexit transition period after leaving the EU with no deal.

The Conservative MP, who was Brexit secretary for two years before resigning in July, was branded “deluded” over an opinion piece which appeared to show he did not understand fundamental aspects of the withdrawal negotiations.

In an article for the Conservative Home website, he wrote: “If we need to leave with no deal and negotiate a free trade agreement during the transition period, so be it. Let’s be clear and honest and tell the EU that’s what we are prepared to do.”

Britain will only enter into a transition phase if the government reaches a withdrawal agreement with the EU. Mr Davis was Brexit secretary when UK and EU negotiators agreed the terms of the transition period, due to run until the end of 2020.

Liberal Democrat MP Layla Moran, of the pro-EU group Best for Britain, said: "These comments by David Davis are completely unbelievable. He is frankly just deluded or just plain stupid.

“It seems like the man who was in charge of delivering Brexit doesn’t understand the process. You can’t have a transition without a deal and everyone knows that.

“The truth is that there are two genuine options available to the parliament and to the country: firstly the government’s deal that loses us decision making power and would leave us worse off, and second, our current deal that would keep our prosperity, keep our say over EU laws and trade agreements and deliver what the majority of people in the UK now want.”

Jon Worth, visiting professor in EU policy at Bruges’s College of Europe, tweeted: “How the sodding hell has Britain had a Brexit Minister (Davis) who does not even understand the basic scheduling of the process? Or is so mendacious or lazy he doesn’t want to understand?”

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Mr Davis’s opinion piece – which he began by quoting a Spice Girls lyric – was published as Tory Brexiteers struggled to gather support for a leadership challenge on Theresa May.

“What we need now is leadership and the courage and confidence to deliver for the UK,” he wrote, claiming “MPs, Party members and the British public are rightly dismayed” with the prime minister’s proposed EU deal.

It is not the first time Mr Davis has been accused of failing to fully understand the Brexit negotiations. Former Irish prime minister Bertie Ahern, speaking about the implications for the Irish border, said in January: “I continue to have my doubts – does he understand this stuff?”

Mr Davis was also widely ridiculed for suggesting three weeks after the EU referendum that Britain would have completed most of its global trade deals “within between 12 and 24 months”.