Nadine Dorries has suggested “sinister forces” were behind the decision not to include her on Boris Johnson’s controversial resignation honours list amid an increasingly bitter war of words with the prime minister.

The former culture secretary used a combative column in the Daily Mail to suggest she was deliberately blocked from receiving a peerage in the House of Lords by “posh boys” working for Rishi Sunak.

Ms Dorries was one of three Johnson allies who believed they were in line to receive a peerage from the outgoing prime minister – but when the list was finally published, their names were absent.

Following the perceived snub, Ms Dorries announced she would stand down as an MP with “immediate effect”, triggering a by-election in her constituency of Mid Bedfordshire.

She was shortly followed by Mr Johnson – who resigned after receiving the findings of the privileges committee investigation into whether he misled MPs over parties in Downing Street – and Nigel Adams, the MP for Selby and Ainsty.

The episode has prompted a war of words between Mr Johnson and his successor, with the former’s camp accusing Mr Sunak of having “secretly blocked” their peerages to avoid the possibility of by-elections – something Downing Street has strenuously denied.

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The feud between the former allies erupted into a bitter public slanging match on Monday, as the prime minister claimed his predecessor asked him to overrule a panel vetting his nominations to the House of Lords.

Mr Sunak said Mr Johnson wanted him “to do something I wasn’t prepared to do”, which was “to either overrule the HOLAC [House of Lords Appointments committee] or make promises to people”.

Hours later, the former Tory leader hit back with a fiery statement of his own, accusing the PM of “talking rubbish”.

Mr Johnson said: “Rishi Sunak is talking rubbish. To honour these peerages it was not necessary to overrule Holac – but simply to ask them to renew their vetting, which was a mere formality.”

Writing for the Daily Mail, Ms Dorries accused those close to Mr Sunak of playing “political games” and that her “absence from the list was deliberate”.

“In the meeting Boris had with Rishi Sunak – a meeting Number 10 initially denied to journalists had taken place – I was told that the PM had indeed assured Boris that he would, in keeping with convention, sign off the list returned to him from Holac,” she wrote.

“What he didn’t say – and what I understand to be true despite denials from those concerned – is that his political secretary, James Forsyth, had made sure that certain names would not be on the Holac list.”

Ms Dorries claimed Mr Forsyth “ensured” her name was not on the list by “failing to pass on vital information” from the vetting body that she needed to agree to stand down from the Commons and join the Lords within six months or face being left off.

“It is my belief that when Rishi Sunak told Boris Johnson he would sign off the list returned to him by Holac, he was using weasel words,” she said. “He already knew who was and wasn’t on that list because he had engineered it via his aide Forsyth.

“I’m not going to lie. I believe sinister forces conspired against me and have left me heartbroken – but that emotion gives me all the strength I need to keep on fighting.”

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In response, the prime minister’s press secretary said: “As is convention, the prime minister forwarded the former prime minister’s peerage list to Holac unaltered.

“Holac then passed back their approved list. The prime minister then accepted Holac’s approved list and forwarded it unamended to the Sovereign for their approval.

“He had no involvement or input into the approved list. It is a point of fact that it is made public by the commission if a prime minister overrules the commission’s advice.”

Holac said on Sunday it would “not comment on individuals” but confirmed it had not supported eight peerage nominees submitted in the former prime minister’s resignation honours.

A spokesperson said: “The commission is advisory to the prime minister and is not involved in the appointment processes after providing advice.

“The commission does not comment on individuals.”