Dominic Cummings has claimed the government originally planned to let coronavirus rip through the country in an attempt to build "herd immunity".
Boris Johnson’s former top adviser said the plan was to develop resistance in the population in the months leading up to September after the disease first emerged in early 2020.
In a series of tweets, he said that it was only abandoned in early March last year after Downing Street was warned that it would lead to a "catastrophe".
Mr Cummings‘ latest intervention comes as he prepares to give evidence to MPs on the Commons health and science committees on Wednesday.
The committees are investigating the government’s response to the pandemic.
Downing Street is braced for a potentially highly damaging onslaught following Mr Cummings’ acrimonious departure from Number 10 at the end of last year.
In a foretaste of what to expect, he said that there may have been no need for any lockdowns if the country had had the "the right preparations and competent people in charge".
Instead he said that at the beginning of March last year, the plan had been "herd immunity" and that claims to the contrary by Health Secretary Matt Hancock were "bull****".
He also strongly attacked the media for accepting the government’s denials.
Mr Cummings wrote in a series of tweets: "Media generally abysmal on coronavirus but even I’ve been surprised by one thing: how many hacks have parroted Hancock’s line that ‘herd immunity wasn’t the plan’ when ‘herd immunity by September’ was ‘literally the official plan in all documents/graphs/meetings’ until it was ditched."
He added: "Yes the media is often incompetent but something deeper is at work: much of SW1 (the Westminster postcode) was happy to believe Hancock’s bull**** that ‘it’s not the plan’ so they didn’t have to face the shocking truth. Most political hacks believe in ‘the system’…
"In week of March 9, No10 was made aware by various people that the official plan would lead to catastrophe. It was then replaced by Plan B. But how ‘herd immunity by September’ could have been the plan until that week is a fundamental issue in the whole disaster."
At the time, the government’s chief scientific adviser, Sir Patrick Vallance, had said that if they tried to suppress the disease "very, very hard" it would simply bounce back when restrictions were released.
Instead he suggested the aim was to "build up some kind of herd immunity" so more people were resistant to the disease and transmission was reduced.
In his tweets, Mr Cummings said there had been "so much lock down (sic) confusion".
He wrote: "Obviously they’re ‘destructive’. But if you have to do it because alternative is ‘hundreds of thousands choking to death and no NHS for months for everybody else and economy sunk because everybody hiding in terror’ then earlier/harder is better for health AND economy.
"If we’d had the right preparations and competent people in charge, we would probably have avoided lockdown 1, ‘definitely’ no need for lockdowns 2 and 3.
"Given the plan was AWOL/disaster and awful decisions delayed everything, lockdown 1 became necessary."
Responding to Mr Cummings’ tweets, a government spokesperson said: "Herd immunity has never been a policy aim or part of our coronavirus strategy.
"Our response has at all times been focused on saving lives and ensuring the NHS was not overwhelmed. We continue to be guided by the latest scientific advice."
Dr Jenny Harries, chief executive of the UK Health Security Agency, said herd immunity was "never" put forward by the government at the beginning of the pandemic.
The former deputy chief medical officer said herd immunity can mean having a successful vaccination programme that makes a population safe and that "has been misinterpreted in many places" as meaning the government would allow people to become infected to develop herd immunity.
"That has never been on the agenda but you would always look to see how safe you can get your population through a vaccination programme," she told the BBC’s Andrew Marr Show.
Home Secretary Priti Patel also denied Mr Cummings’ claim, telling the BBC "absolutely not" when asked if it was true.