Downing Street has denied that Boris Johnson takes “power naps” during the working day.
The firm rebuttal came after a report in The Times that it was not uncommon for the prime minister to “shut the door and have a kip”.
The report sparked speculation over whether Mr Johnson was suffering from broken sleep at night since the birth of his youngest child Wilfred last April.
But the PM’s press secretary Allegra Stratton said that the claim was “untrue”.
She told reporters at a daily Westminster media briefing: “He doesn’t have a nap during the day when he is at Downing Street.
“His day is jam-packed from early in the morning to late in the night. There is no gap for anything like that.”
Ms Stratton declined to comment on whether the PM’s nights were disrupted by Wilfred.
The claim emerged in a report for Times Radio on how Mr Johnson’s working day compares with those of his predecessors at No 10.
It quoted an unnamed “Downing Street insider who knows the prime minister well” as saying: ”It would not be entirely uncommon in the diary for him to shut the door and have a kip for half an hour or so -Â a power executive business nap to get him ready for the rest of the day.”
The report said that Mr Johnson was an early riser, going jogging at 6am in Buckingham Palace’s gardens before getting down to work.
But it said that he routinely turns up 10 minutes late for meetings, with one official saying: "He keeps his own time.”
According to the report, Mr Johnson often spends more than 12 hours in his office before retiring to his flat above No 11, where he can expect to have at least two red boxes of paperwork to read before going to bed.