Nadine Dorries has warned the Tories with Rishi Sunak in No10 they are heading into a "cold and brutal wasteland" in opposition.
The ex-Cabinet minister also claimed her party would "die" if former Prime Minister Boris Johnson does not return as leader.
It comes just days after the Tory MP - a staunch loyalist of Mr Johnson - accused Mr Sunak of dumping key Conservative policies of the past three years.
Just days ago the Government confirmed it would scrap controversial plans drawn up by Ms Dorries as Culture Secretary to privatise Channel 4.
But in a bitter escalation, Ms Dorries said: "With Rishi in No10, we are heading into the long, cold and brutal wasteland of thankless opposition".
The former minister, who has reportedly been nominated for a peerage by Mr Johnson, also described her former boss as a "political rock star".
While Mr Johnson won a landslide victory in 2019, his popularity plummeted during the fallout of multiple scandals, including Partygate.
Writing in the Mail on Sunday, she added: "For the Conservatives, it's bring back Boris or die because the first task of any Labour government would be to ensure that there'll never be a majority Conservative government ever again."
Speaking on the BBC's Sunday with Laura Kuenssberg, Mr Sunak dodged a question over whether the Tories faced a 1997-style wipeout at the next election.
Instead, he said his focus was on delivering on the five pledges he set out last week, including slashing inflation and the record NHS-backlog.
"What the country wants is a Government that is focused on the things that matter to them," he said.
Pressed on his colleagues who would like to see a comeback for Mr Johnson, the PM added: "I think what everyone in our party wants is the country's priorities to be met.
"And they want the Conservative Party and the Conservative Government to do a good job of delivering for the British people. This year people will see us really work our socks off to deliver for them".
A spokesperson for Mr Johnson told The Sunday Times: “Boris Johnson is fully supporting the government. He urges the Conservative Party to unite, deliver on the promises of the 2019 election, and beat Starmer.
"He continues to campaign on issues such as Ukraine, Brexit and levelling up, both in his constituency and in parliament.”
