David Cameron has been slammed by a backbench Tory MP, who blamed him for the rise of Ukip and called for a vote of no confidence in his leadership.
North West Leicestershire MP Andrew Bridgen revealed last night he had sent a letter to the party's powerful 1922 committee calling for a ballot.
In a brutal assessment, he warned that the Prime Minister had a "credibility problem", adding in an article for the Mail on Sunday: "The voters think we have many of the right messages - they just don't believe the messenger."
A leadership battle is automatically triggered when 46 MPs lodge letters with the 1922 committee.
Last month, a Conservative rebel told The Huffington Post UK that at least 30 Tory MPs had signed letters.
Bridgen is only the second to be publicly identified as having sent a missive. Patrick Mercer recently resigned the Tory whip amid allegations he broke lobbying rules - rendering his letter invalid.
The news comes after a poll commissioned by Tory peer Lord Ashcroft suggested that, for the first time, Mr Cameron trails his party for popularity.
Bridgen said he regretted having to urge a no confidence vote. But he insisted: "I have come to the view that although many of our policies are right, whether on welfare reform or reducing the deficit, there is a credibility problem with the current leader.
"The voters think we have many of the right messages - they just don't believe the messenger...
"By pressing ahead with gay marriage and delaying a promise on an EU referendum until he was forced to do so, Mr Cameron has fuelled the rise of the UK Independence Party (Ukip).
"We have created our own nemesis."
Bridgen referred to the row over a senior Tory figure allegedly describing party activists as "swivel eyed loons".
"I know No 10 denied that anyone close to the Prime Minister regarded ordinary party members as 'swivel-eyed loons'," he said.
"But I am afraid that some people at the top of the party do perceive Tory grassroots activists in this way."
The MP - who refused to say whom he wanted to replace Mr Cameron - admitted that some thought it was the wrong time for a leadership challenge.
But he compared the situation to being in an aeroplane with a pilot who did not know how to land.
"We can either do something about it before the crash or sit back, watch the in-flight movies and wait for the inevitable," he added.
Speaking on the BBC's Marr Show on Sunday morning, Foreign Secretary William Hague dismissed the story.
Cameron is a "brilliant" Prime Minister, he said, adding: "He is someone who does a fantastic job for this country."