Chief backbench Eurosceptic Jacob Rees-Mogg has submitted a letter of no confidence in the prime minister, taking Theresa May’s leadership closer to the brink of collapse.

Mr Rees-Mogg, who chairs the Brexit backing European Research Group (ERG), said he was specifically choosing to make his letter public in a sign that he wants other colleagues to consider following his lead.

It came at the end of meeting of the ERG in which others, though not all, called for further letters of no confidence to be sent in – prominent Eurosceptic Steve Baker emerged from the room demanding a new party leader.

Under Tory rules, once 48 letters are handed in to the chair of the backbench 1922 Committee there must be a vote of no confidence in the party leader.

In a statement after the meeting, Mr Rees Mogg denied he was instigating a coup, saying: “It’s using the proper procedures of the Conservative party when the policy that has come forward does not meet our promises to our voters.

“The Conservative party [manifesto] on which all Conservative MPs stood said specifically that we would leave the customs union.

“It did not have any small print that said, ‘oh unless we decide to have a backstop that is a permanent customs union’, that is harder to leave than leaving the European Union under Article 50.”

In Mr Rees-Mogg’s letter he acknowledged that he could have kept it confidential, but said he was choosing to make it public, with his statement outside parliament coming a few moment later.

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He argued that the deal secured by the prime minister was “not Brexit”, before saying: “What we need is a leader who will say to the European Union ‘it is impossible to divide up the United Kingdom, it is impossible to agree to a situation where we will have a perpetual customs union, it is impossible to pay £39bn of taxpayers’ money for a few promises.”

The backbencher denied his statement was a reflection of his own personal ambition to be the new Tory leader, adding that he was not putting his own name forward for the job.

But at the ERG meeting he arrived from, in House of Commons Committee Room 10, his own speech had been met with a loud banging of the desks.

Surrounded by a huge scrum of journalists, he made his way to give a statement outside the Palace of Westminster, but he would not be drawn on whether the ERG yet had the numbers needed to force a confidence vote.

He and others did however call for for Ms May to go, with Mr Mogg saying: “I think there are many people in the Conservative Party, not just in parliament but in the country, that feel her services now should come to an end.

“She is a very dutiful person, she has served the country to the best of her ability but she has let us down in this deal and has not delivered on what she has said she would do.”

Ex-minister Steve Baker was also among those calling for change, saying: “We’ve tried everything to change policy but not the prime minister, but it has not worked.

“It is too late – we need a new leader.”

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He also later confirmed that he had sent in a letter of no confidence to Sir Graham Brady, the chair of the 1922 Committee. Boris Johnson also spoke at the ERG meeting, but had kept a noticeably low profile on a day that might be critical to his own leadership ambitions.

Other MPs told the 40-odd journalists outside the ERG meeting that they had also handed in letters of no confidence, but dissent was not uniform – with some saying they would refuse to topple the PM.

It’s using the proper procedures of the Conservative party when the policy that has come forward does not meet our promises to our voters Jacob Rees-Mogg MP

A vote of sorts, seen from the outside, showed only a third of those inside raise their hands – though it was not clear exactly what they were voting on.

Foreign Office minister Alistair Burt, a loyalist, told journalists outside the room that he would be urge colleagues not to attempt to overthrow the PM, warning that the public would be “amazed” if Tory MPs forced a leadership contest at this time.

The Independent understands that the critical number of letters had still not been reached by Thursday afternoon. If and when it is, protocol would see Sir Graham inclined to meet and consult with Ms May before holding a vote of no confidence at the “earliest possible opportunity”.

Ms May’s deal came under a hail of criticism in the House of Commons, where only a handful of Tories spoke in favour of an agreement thrashed out in 19 months of intensive negotiations.

Theresa May: 'The choice is clear: we can leave with no deal, risking no Brexit at all'

There was laughter from opposition benches when the PM said her deal would allow the UK to leave the EU “in a smooth and orderly way” on 29 March.

Ms May insisted the deal was in the national interest and offered a future relationship with “a breadth and depth of cooperation beyond anything the EU has agreed with any other country”.

In a swipe at her Brexit-backing critics, she said the EU would never accept any agreement which did not involve a “backstop” arrangement to ensure the Irish border remains open.

Ms May said it would be “entirely irresponsible” for the government to have simply torn up the backstop.

“The Brexit talks are about acting in the national interest and that means making what I believe are the right choices, not the easy choices,” she said.