Boris Johnson ally Nadine Dorries is facing a potential investigation over alleged “communications” she made to civil servants regarding her thwarted peerage.
Cabinet Secretary Simon Case said he had referred the messages Ms Dorries allegedly sent to senior civil servants to Tory chief whip Simon Hart and Commons Speaker Lindsay Hoyle.
He said he had also sought legal advice over the matter.
It comes as Ms Dorries, who served as culture secretary under Mr Johnson, announced she had written a book on the “political assassination” of Boris Johnson due to be released days before the Tory party conference in October.
Ms Dorries was one of three Johnson allies who believed they were in line to receive a peerage from the outgoing prime minister last month – 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.
However, Ms Dorries later said she would not formally resign until she received answers from Downing Street as to why she did not get her peerage.
In a session of the public administration and constitutional affairs committee, Tory MP and chair William Wragg asked Mr Case about the “lingering member for Mid Bedfordshire”.
“Obviously, the most recent sets of resignation honours and particularly peerages has excited some public comment, and indeed, some current former and indeed lingering members of the House of Commons as well,” he said.
“Are you aware of any forceful communications – it may be described – sent by the lingering member for Mid Bedfordshire to senior civil servants?”
He continued: “Really – I suppose, threatening it could be described – to use the platform of the Commons and indeed her own television programme to get to the bottom of why she hadn’t been given a peerage?”
Mr Case said he was “aware” of such communications and had flagged them to the Commons Speaker and Conservative chief whip.
Asked if he had taken legal advice on whether the Honours (Prevention of Abuses) Act 1925 could “come into play”, Mr Case said he was “seeking further advice on that question”.
Sky News has approached Ms Dorries for comment but has not received a reply.
Liberal Democrat Deputy Leader Daisy Cooper said the latest claims against Ms Dorries were “staggering”.
“It’s crucial a swift investigation takes place into whether Nadine Dorries may have broken the law.
“Not only is Dorries failing to represent the people of Mid Bedfordshire, but now it emerges she has allegedly sent threatening messages to civil servants.
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Ms Dorries received £20,500 as a partial advance from HarperCollins for the book, which she said tells the story of “treachery and deceit at the heart of the Westminster machine”.
It is set to hit the stands on 28 September – just three days before Conservatives convene for the annual party conference on 1 October.
She said: “I had wanted to discover the forces behind the downfall of the prime minister. Instead, I found a fault line within the Conservative Party stretching back decades, and a history of deception fuelled by the darkest political arts.
“If you thought that power flowed from the people into parliament, be prepared to think again.”
Last month, Ms Dorries was one of seven MPs who were heavily criticised by the privileges committee for putting “improper pressure” on its investigation into whether Mr Johnson lied to MPs over partygate.