Former Conservative minister Nadine Dorries has announced she is resigning, after months of criticism over her absence from the House of Commons.
In her resignation letter, the Tory MP accused Rishi Sunak of "demeaning his office by opening the gates to whip up a public frenzy" against her.
The letter to the prime minister, published in The Mail on Sunday, said: "It has been the greatest honour and privilege of my life to have served the good people of Mid Bedfordshire as their MP for 18 years and I count myself blessed to have worked in Westminster for almost a quarter of a century.
"Despite what some in the media and you yourself have implied, my team of caseworkers and I have continued to work for my constituents faithfully and diligently to this day."
The letter went on to say Mr Sunak had abandoned "the fundamental principles of Conservatism" and "history will not judge you kindly".
Ms Dorries, a key ally of Boris Johnson, said she was resigning with "immediate effect" on 9 June after she failed to get a peerage in Mr Johnson's resignation honours list.
But having not formally vacated her seat, a by-election has not been able to take place.
Ms Dorries said she was delaying her exit to investigate why she was refused a seat in the House of Lords.
In the letter she said her "investigations focused on the political assassination of Boris Johnson" but as they continued a "dark story emerged which grew ever more disturbing with each person I spoke to".
She claimed that she felt "remaining as a backbencher was incompatible with publishing a book which exposes how the democratic process at the heart of our party has been corrupted". As such she wanted to keep her parliamentary privilege until today.
Meanwhile both Flitwick Town and Shefford Town Council in her Bedfordshire constituency formally called for her to resign.
The town clerk for Flitwick Town Council said that her "focus appears to have been firmly on your television show, upcoming book and political manoeuvres to embarrass the government for not appointing you to the House of Lords" instead of "representing your constituents".
In a Mail on Sunday video she described accusations of her abandoning her constituents as "nonsense".
Following the letter, a Conservative Party spokesman said the party has already "selected a candidate and are ready for the by-election campaign".
Ms Dorries also accused Mr Sunak of leading attacks on her resulting in "the police having to visit my home and contact me on a number of occasions due to threats to my person".
"The clearly orchestrated and almost daily personal attacks demonstrates the pitifully low level your government has descended to," she wrote.
Attacking the prime minster's record, she added: "Since you took office a year ago, the country is run by a zombie parliament where nothing meaningful has happened.
"You have no mandate from the people and the government is adrift. You have squandered the goodwill of the nation, for what?
"Your actions have left some 200 or more of my MP colleagues to face an electoral tsunami and the loss of their livelihoods, because in your impatience to become prime minister you put your personal ambition above the stability of the country and our economy.
"Bewildered, we look in vain for the grand political vision for the people of this great country to hold on to, that would make all this disruption and subsequent inertia worthwhile, and we find absolutely nothing."
Labour and the Lib Dems are hopeful of overturning Ms Dorries' 24,000 majority in Mid Bedfordshire, which has been held by the Conservatives since 1931.
Lib Dem leader Sir Ed Davey said in a statement: "The people of Mid Bedfordshire deserve better than this circus act that has followed the Conservatives these past few months." Downing Street has not commented.
Speaking to Sky News, Labour's shadow Northern Ireland secretary Peter Kyle said the party is "relieved for residents across Mid Bedfordshire".
"This is good news for them. They've wanted to have this by-election so they can move forward but they've been held back by this civil war that is raging at the heart of the Conservative Party," he said.
"It doesn't surprise me that the letter she's written is excoriating. It doesn't surprise me because Rishi Sunak has been having a go at her recently.
"But while the Conservatives are rowing with each other, we in the Labour Party have our candidate Alistair Strathern, whose been working his socks off since June, in place, so we can prepare a hard-working alternative."