Matt Hancock showed "nuclear levels" of confidence at the start of the COVID pandemic - and "regularly" told colleagues in Downing Street things "they later discovered weren't true" - according to a senior civil servant who was there at the time.
Helen MacNamara was deputy cabinet secretary during the pandemic and was giving evidence to the COVID inquiry today.
Asked about the then health secretary, she mentioned "jarring" behaviour she had seen, including him miming playing cricket and saying "they bowl them at me, I knock them away" during the first lockdown.
Ms MacNamara said this was an example of the "unbelievably bullish" and dismissive culture present during Boris Johnson's tenure as prime minister as the COVID-19 crisis hit the UK.
Mr Johnson showed a "breezy confidence", dismissing warnings Ms MacNamara supplied to him, she told the inquiry.
She added that within Downing Street people were "laughing at the Italians" during the initial outbreak there.
Italy was among the European countries first hit by the virus - leading to shocking scenes in the north of the country, as Sky News reported at the time.
Questions about Mr Hancock grew within Number 10 in April 2020, and there was a "lack of confidence of what he said was happening, was actually happening".
This included Mr Hancock saying things were under control or being sorted in meetings, only for it to emerge in days or weeks that "was not in fact the case".
There was a "pattern of being reassured that something was absolutely fine and then discovering it was very, very far from fine", she said.
Andrew O'Connor KC, the lawyer for the inquiry, asked Ms MacNamara: "Does it come back to the fact that Mr Hancock regularly was telling people things that they later discovered weren't true?"
"Yes," she replied.
'Jarring' moment 'really stuck with' civil servant
Ms MacNamara added that she returned to Downing Street after suffering from COVID in April 2020 and found it "eerily empty" - although Mr Hancock was present.
She said she told Mr Hancock he did not need to be there, and that it must be "very hard" being health secretary in a global pandemic.
Apparently, Mr Hancock told her he was "loving" the responsibility - and to show this, he took up a "batsman's stance outside the cabinet room".
Mr Hancock then said "they bowl them at me, I knock them away", according to Ms MacNamara.
She told the inquiry: "I'm trying to explain just how jarring some of that was.
"It does partly go back to my point about the nuclear levels of confidence that were being deployed, which I do think is a problem. It really stuck with me, this moment."
She described it as "overconfidence".
A spokesman for the former health secretary said: "Mr Hancock has supported the inquiry throughout and will respond to all questions when he gives his evidence."