Robert Courts, who took over the Witney constituency that used to be held by David Cameron, stood down from his role as a parliamentary private secretary at the Foreign Office to allow him to vote against the Government in the Commons tonight.
His exit follows the resignations of Boris Johnson, David Davis, Steve Baker and Greg Hands from ministerial jobs – and Maria Caulfield and Ben Bradley from party roles – over the Brexit row.
Mr Courts announced his departure on Twitter last night, expressing opposition to the Brexit plan agreed by the Cabinet in a meeting at Chequers.
He wrote yesterday: “I have taken very difficult decision to resign position as parliamentary private secretary to express discontent with Chequers in votes tomorrow.
“I had to think who I wanted to see in the mirror for the rest of my life. I cannot tell the people of West Oxon that I support the proposals in their current form.”
Mr Courts became a parliamentary private secretary, often seen as the lowest rung on the frontbench ladder, last January. At the time he said he was ‘delighted’ at this appointment.
He was elected to the Commons in a by-election in October 2017 and re-elected with an increased majority of more than 21,000 votes at the general election last year. He voted to Leave the EU in the 2016 referendum on the UK’s membership of the bloc.
Theresa May has appealed to warring Tory MPs to back her controversial blueprint for Brexit and avoid a disorderly withdrawal from the EU which would damage Britain’s interests.
Ahead of a crucial week in Parliament, the Prime Minister acknowledged feelings in the party were running high, but said her plan offered a “hard-headed and practical” way forward.
However leading Brexiteer Jacob Rees-Mogg warned trust in Mrs May was waning amid acrimonious claims key ministers, including David Davis, were kept in the dark about her proposals.
In a scathing aside, he accused her of failing to embrace the opportunities of Brexit, saying she was “a Remainer who remained a Remainer”.
Mrs May meanwhile revealed Donald Trump’s advice to her on the Brexit negotiations had been to “sue the EU”.
On Monday, MPs will vote on a series of amendments to the Customs Bill tabled by members of the European Research Group (ERG), which Mr Rees-Mogg leads, intended to scupper her plans for a “UK-EU free trade area” based on a “common rule book”.
With no Labour backing, the changes stand little chance of getting through, although the votes could provide Conservative Brexiteers with the opportunity to stage a show of strength in Parliament.
Meanwhile Boris Johnson, who quit as foreign secretary in protest after the plan was agreed by the Cabinet at Chequers, was reported to be preparing to make a resignation statement in the Commons, providing another potential flashpoint.
Mrs May could then face a further challenge on Tuesday, this time from pro-EU Tories seeking to amend the Trade Bill to keep the UK in a customs union with the EU, although it is unclear whether they will now put it to a vote.
The Prime Minister said she had been forced to come forward with the revised proposals after the EU had offered two options, either remain in the customs union and accept continued freedom of movement or see Northern Ireland effectively “carved out” from the UK, neither of which was acceptable.
“Faced with that we had an option.
“We could go for no deal, no deal is still there, it is still possible, but I think the best thing for the UK is to have deal that sets a good relationship with our trading partners in the future,” she told BBC1’s The Andrew Marr Show.
“So if we were going to find something that was Britain’s interest, that delivered on the referendum and that was negotiable, we had to make what is a compromise but is a positive in terms of the benefits it gives us.”
She said the plan would avoid the need for a hard border between Northern Ireland and the Republic, maintain “frictionless” trade with the EU, and still allow the UK to negotiate free trade deals with other countries.
“Many people voted from the heart to leave the European Union,” she said.
“My job as Prime Minister is to deliver for them, but also I’ve got to be hard-headed and practical about this and do it in a way that ensures we get the best interests for the UK.”
However Mr Rees-Mogg said her approach to the Brexit negotiations had been “hopeless”, giving too much ground to Brussels and abandoning her previous red lines.
While he played down the prospect of an imminent leadership challenge, he warned Mrs May risked splitting the party unless she was prepared to change course.
“Brexit is enormously positive, a huge opportunity for the country. I’m afraid the Prime Minister doesn’t see that.
“It is why I think she is a Remainer who has remained a Remainer,” he told BBC1’s Sunday Politics.
“It is a worry that the Prime Minister was so clear that Brexit meant Brexit and that she had her red lines and these have now gone.
“Trust is to some extent at the heart of policy making so that does concern me.”
Earlier former Brexit minister Steve Baker, who quit along with Mr Johnson and Mr Davis, said the Chequers plan was drawn up in the Cabinet Office while the Department for Exiting the EU had been reduced to a sham, “Potemkin structure”.
“An establishment elite who never accepted the fundamental right of the public to choose democratically their institutions are working towards overturning them,” he told The Sunday Telegraph.