Justice secretary David Gauke has resigned shortly after Boris Johnson was confirmed as the next Prime Minister.
It marks a turbulent start to Mr Johnson’s predicted stint at Number 10, with a number of cabinet ministers have indicating they will quit their posts rather than waiting to be sacked by the new PM.
Mr Gauke tweeted his decision, saying it had been ‘an honour’ to serve in Theresa May’s cabinet.
Congratulations @BorisJohnson on being elected as Leader of @Conservatives and PM @10DowningStreet. An honour to serve in Cabinet @MoJGovUK, @DWP and @hmtreasury under @theresa_may. Looking forward to returning to backbenches tomorrow, serving people of South West Hertfordshire.
— David Gauke (@DavidGauke) July 23, 2019
Earlier he told presenter Nick Ferrari on LBC radio he would hand his letter of resignation to Theresa May shortly after her final Prime Minister’s Questions on Wednesday.
He said he could not back Mr Johnson’s plan for a no-deal Brexit, but ruled out voting against the new government in a no-confidence vote.
“I strongly believe that we should not leave without a deal and that's why I am resigning,” he said. “What I have said consistently is that I will not vote against the government in a confidence vote."
Earlier on Tuesday, Mr Gauke told BBC Radio 4’s Today programme there were "parliamentary mechanisms" which could prevent the UK from leaving the EU without a deal by October 31.
Mr Gauke stressed that he would not vote against a Tory government in a motion of no confidence if it was heading towards a no-deal Brexit, but said: "I don't think it will come to that. I think that there will be parliamentary mechanisms.
"There is a clear majority in the House of Commons that doesn't want to leave the EU without a deal, I think that will become very clear in the autumn."
He added there was the possibility of a "period of huge uncertainty" in Westminster as the October 31 deadline approaches.
"Are there circumstances where there is a risk of a government losing a confidence motion? Yes, clearly there are circumstances where there is a risk that that might happen.
"I think that the new prime minister would be wise to avoid getting into those circumstances."
His comments come a day after international development secretary and former Tory leadership candidate Rory Stewart said he could not work under Mr Johnson.
Education minister Anne Milton resigned on Tuesday, saying that she has "grave concerns about leaving the EU without a deal".
And Sir Alan Duncan quit as Foreign Office minister in protest at his expected victory, predicting a "crisis of government" if Mr Johnson becomes prime minister.
Chancellor Philip Hammond has also given notice that he will resign rather than serve under Mr Johnson.
The expected resignations would leave Mr Johnson with a Tory-DUP majority of just two, after Dover MP Charlie Elphicke had the Conservative whip suspended when he was charged with sexually assaulting two women.
The Government majority could be further reduced next week to just one if the Conservatives lose the Brecon and Radnorshire by-election.
It means Mr Johnson’s new government would be at serious risk of immediate collapse in the event of a no-confidence vote in Parliament.
On Monday, Mr Stewart ruled out working with Mr Johnson, telling LBC: "I think the danger is the lack of detail, the lack of anything particular. It's the vagueness, the abstraction, the blandness of it that worries me.
"I literally don't know what happens on the 31st October. I can't plot his path.
"My mind works by trying to do a little decision tree. I don't see how he can get no-deal through parliament. I don't see how he can deliver something that can simultaneously please Amber Rudd and Mark Francois. I don't get it.
"He's not dangerous in the sense that he is a 1930s figure. It's just that I don't get him. He's just not my kind of person."