Matt Hancock has said he was warned the COVID pandemic could kill hundreds of thousands of people in the UK two months before the country was put into lockdown and claims ministers "did not really believe it".
The former health secretary said the chief medical officer for England, Professor Sir Chris Whitty, informed him in January 2020 that, in a "reasonable worst case scenario", as many as 820,000 could die.
Mr Hancock said when he passed on the warning to other ministers at a cabinet meeting three days later, the reaction was "shrug shrug" as they did not really believe it.
The details are revealed in Mr Hancock's Pandemic Diaries: The Inside Story Of Britain's Battle Against Covid, serialised in the Daily Mail and The Mail+.
He said that on 17 January, Sir Whitty warned that there was a "50:50" chance that the virus would reach Britain and laid out the figures.
"The whole room froze. We are looking at a human catastrophe on a scale not seen here for a century."
However, when he shared the warning with a Brexit Day meeting of the Cabinet on 31 January, he said it was met largely with indifference.
"The reaction was somewhat 'shrug shrug' - essentially because they didn't really believe it. I am constantly feeling that others, who aren't focused on this every day, are weeks behind what's going on," he said.
Johnson: 'It will probably go away'
Mr Hancock also suggested that Boris Johnson had been reluctant to engage on the issue.
When he first raised the outbreak in China with him in early January, his response had been: "You keep an eye on it. It will probably go away."
A month later he said he warned Mr Johnson that while it might still be possible to contain the virus, it was "more likely we're going down". The reply, he said, was simply: "Bash on."
More than 200,000 people with COVID have died in the UK, figures show.
The details were released as Mr Hancock returned to Westminster for the first time after his controversial appearance on I'm A Celebrity ... Get Me Out Of Here!
Hancock defends release of care home residents
Mr Hancock also defended his handling of the controversial decision to release care home residents from hospital without testing, which was blamed for thousands of deaths.
On 2 April, he noted: "The tragic but honest truth is we don't have enough testing capacity to check anyway. It's an utter nightmare, but it's the reality."
In April, the High Court ruled the government acted unlawfully by discharging untested hospital patients into care homes during the early stages of the pandemic.
The first national lockdown began on 23 March 2020.