Theresa May has been hit by another resignation as Tory MPs continue to protest against her Brexit plans ahead crunch votes in the Commons.

Robert Courts has become the latest ministerial aide to quit the Government in protest at the Chequers plan, which has prompted criticism from hard Brexiteers.

The MP for Witney – David Cameron’s former seat – said on said on Twitter: “I have taken very difficult decision to resign position as PPS 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 WOxon that I support the proposals in their current form.”

The Prime Minister faces threats of Commons revolts this week by pro- and anti-EU MPs that risks undermining any chances of a deal with Brussels.

Last week, May was forced to reshuffle her top team after Boris Johnson quit as Foreign Secretary, David Davis resigned as Brexit Secretary and Steve Baker walked out as a junior Brexit Minister.

The next day, Mansfield MP Ben Bradley and Lewes MP Maria Caulfield  resigned as Vice-Chairs of the Conservative Party in opposition to the policy.

Earlier on Sunday, May warned Tory rebels they could be left with “no Brexit at all” unless they fall into line.

In an article for The Mail on Sunday, she called for MPs to take a “practical and pragmatic” approach rather than face a “damaging and disorderly” Brexit.

But ministers who quit the Government over her negotiating stance attacked the Prime Minister in other Sunday papers – with Davis accusing her of making an “astonishingly dishonest claim” that Brexiteers had not come up with an alternative to her plan. 

Baker claimed the Brexit Department was little more than a “Potemkin structure to [distract from] what the Cabinet Office Europe unit was doing for the Prime Minister.” 

Speaking on the BBC’s Andrew Marr Show on Sunday morning, May hit back at the claims, saying: “Let me very clear that no department was cut out of these discussions. Discussions have been taking place for some considerable time…We have been discussing this option.”

Writing in the Mail on Sunday, May acknowledged some MPs had concerns about her plan for a “common rule book” with the EU for goods and customs traded within what she called a new “UK-EU free trade area”.

However, she insisted that she had yet to see a “workable alternative” to the proposals – agreed by the Cabinet at Chequers – that would ensure trade remained as “frictionless” as possible while avoiding the return of a hard border between Northern Ireland and the Republic.

“We need to keep our eyes on the prize. If we don’t, we risk ending up with no Brexit at all,” she said.

“I know there are some who have concerns about the ‘common rule book’ for goods and the customs arrangements which we have proposed will underpin the new UK-EU free trade area. I understand those concerns.

“But the legacy of Brexit cannot be a hard border between Northern Ireland and Ireland that unpicks the historic Belfast Agreement.

“It cannot be the breaking up of our precious United Kingdom with a border down the Irish Sea. And it cannot be the destruction of integrated supply chains and just-in-time processes on which jobs and livelihoods depend.”