David Gauke, the justice secretary, will quit the Government on Wednesday if Boris Johnson becomes prime minister.

Mr Gauke, who has served in Theresa May‘s cabinet since she took office in June 2016, said he would not be able to serve under the former foreign secretary if he pursues a no-deal Brexit.

As the Tory leadership contest enters its final 48 hours, the prominent no-deal critic told the Sunday Times that crashing out of the European Union would lead to national “humiliation”.

And Mr Gauke said: “Given that I’ve been in the Cabinet since Theresa May came to power, I think the appropriate thing is for me to resign to her.”

The paper also reported that up to six Tory MPs are considering defecting to the Liberal Democrats should Mr Johnson beat his rival Jeremy Hunt and enter Number 10 – leaving him with no majority in the Commons.

Biggest lies told by Boris Johnson Show all 5 1 /5 Biggest lies told by Boris Johnson Biggest lies told by Boris Johnson Made-up quote for The Times Johnson was sacked from The Times newspaper in the late 1980s after he fabricated a quote from his godfather, the historian Colin Lucas, for a front-page article about the discovery of Edward II’s Rose Palace. “The trouble was that somewhere in my copy I managed to attribute to Colin the view that Edward II and Piers Gaveston would have been cavorting together in the Rose Palace,” he claimed. Alas, Gaveston was executed 13 years before the palace was built. “It was very nasty,” Mr Johnson added, before attempting to downplay it as nothing more than a schoolboy blunder. PA Biggest lies told by Boris Johnson Sacked from cabinet over cheating lie Michael Howard gave Boris Johnson two new jobs after becoming leader of the Conservatives in 2003 – party vice-chairman and shadow arts minister. He was sacked from both positions in November 2004 after assuring Mr Howard that tabloid reports of his affair with Spectator columnist Petronella Wyatt were false and an “inverted pyramid of piffle”. When the story was found to be true, he refused to resign. PA Biggest lies told by Boris Johnson Broken promise to boss In 1999 Johnson was offered editorship of The Spectator by owner Conrad Black on the condition that he would not stand as an MP while in the post. In 2001 he stood - and was elected - MP for Henley, though Black did allow him to continue as editor despite calling "ineffably duplicitous" PA Biggest lies told by Boris Johnson Misrepresenting the people of Liverpool As editor of The Spectator, he was forced to apologise for an article in the magazine which blamed drunken Liverpool fans for the 1989 Hillsborough disaster and suggested that the people of the city were wallowing in their victim status. “Anyone, journalist or politician, should say sorry to the people of Liverpool – as I do – for misrepresenting what happened at Hillsborough,” he said. PA Biggest lies told by Boris Johnson ‘I didn’t say anything about Turkey’ Johnson claimed in January, that he did not mention Turkey during the EU referendum campaign. In fact, he co-signed a letter stating that “the only way to avoid having common borders with Turkey is to vote Leave and take back control”. The Vote Leave campaign also produced a poster reading: “Turkey (population 76 million) is joining the EU”

The ballot for the Tory leadership race will close on Monday, with the result announced the following day.

Mr Johnson, who is widely predicted to win the contest, has reportedly been secretly wooed by European politicians and officials in a bid to thrash out a new Brexit plan to avoid a no-deal exit, the Sunday Times reported.

It said figures from Ireland, France, Germany, Belgium and the Netherlands had established contact with the frontrunner’s team and signalled their intention to do a deal.

Amber Rudd, the work and pensions secretary and former Remainer, urged her Tory colleagues to back whoever wins the contest.

Writing in the Sunday Telegraph, she said: “Just as the Conservative Party came together after that EU referendum, it must now come together again no matter who wins.

“I know many of my colleagues have strong feelings but a new prime minister will get a new hearing in the European Union and I hope everyone can unite behind that.

“If we don’t, the alternative could be Corbyn for Christmas.”

Boris Johnson blimp flies over Parliament Square as anti-Brexit protesters gather for major march

Her comments came after Philip Hammond, the chancellor, fired a warning shot to Mr Johnson, saying he would do “everything in my power” to block a no-deal Brexit and left open the possibility of voting to bring down a Conservative government in such an event.