Labour has demanded an independent inquiry into reports about Jeremy Corbyn's health.
The party has responded to a story in the Times on Saturday, which alleged Mr Corbyn was "too frail" to lead, and was attributed to civil service sources.
The report said the 70-year-old leader of the opposition is being "propped up" by his advisers and expressed concern at the prospect of him becoming prime minister.
One senior civil servant told the newspaper: "When does someone say (he) is too ill to carry on as leader of the Labour Party let alone prime minister?"
Jon Trickett MP, Labour's shadow minister for the Cabinet Office, described the report as a "totally unwarranted" political intervention with "disturbing implications for our democratic system".
Mr Trickett has written to civil service chief Mark Sedwill requesting a meeting to discuss the "credible account" in the newspaper of an "apparent breach of civil service neutrality".
Read more of today's stories here
He said: "The premise of these conversations is the allegation that Mr Corbyn's health is poor. This is manifestly untrue.
"Discussion of these matters, based on false assumptions, should not be taking place.
"Worse, it is without precedent in my experience that any high-level discussion about senior politicians, let alone the leader of the opposition, should be shared with a newspaper."
Speaking on the BBC's Andrew Marr Show earlier, Unite the Union boss Len McCluskey attacked journalists for "fake news" over the report claiming Mr Corbyn was mentally and physically unfit for office, possibly due to a stroke.
"They ought to be ashamed of themselves," he said. "It was fake news, it was lies, it was distortion.
"Jeremy Corbyn is fit as a fiddle, he is one of the strongest people I have ever met - people 20 years younger struggle to keep up with him...
"I don't believe them at all - it's the Murdoch press, of course they are going to attack and try to undermine Jeremy."
