Britain's government "disastrously" failed the public by mishandling its coronavirus pandemic response, former top adviser Dominic Cummings told lawmakers on Wednesday, calling Prime Minister Boris Johnson "unfit for the job".

"Tens of thousands of people died who didn't need to die," Cummings, an abrasive political strategist who masterminded Brexit, said in an excoriating account that blamed senior ministers and officials including himself for getting it wrong at the outset.

Cummings said Johnson was recklessly insouciant in the early days of the crisis in February 2020, even volunteering to get infected with Covid-19 live on television to show there was nothing to fear.

Cummings (R) has launched a series of attacks against his former boss's coronavirus policies and financial dealings
Cummings (R) has launched a series of attacks against his former boss's coronavirus policies and financial dealings AFP / DANIEL LEAL-OLIVAS

But he said that even after nearly dying himself from the virus weeks later, the prime minister declined to learn from mistakes and ignored scientists' advice in September to introduce a second lockdown, leading to many more deaths over winter.

Covid-19 has claimed nearly 128,000 lives in Britain -- the fifth-highest official death toll in the world, and the highest in Europe.

"The truth is that senior ministers, senior officials, senior advisers like me fell disastrously short of the standards that the public has a right to expect of its government in a crisis," Cummings told a parliamentary committee.

Johnson's government has overseen a successful vaccination drive, with more than two-thirds of adults getting at least one dose
Johnson's government has overseen a successful vaccination drive, with more than two-thirds of adults getting at least one dose AFP / Oli SCARFF

He described political leadership during the crisis as "lions led by donkeys over and over again".

"When the public needed us most the government failed," he said, apologising "to all the families of those who died unnecessarily".

Cummings has also accused Health Secretary Matt Hancock of lying about the government's true plans for the pandemic
Cummings has also accused Health Secretary Matt Hancock of lying about the government's true plans for the pandemic AFP / Tolga Akmen

In response, Johnson told parliament he took "full responsibility" but insisted decision-making during the pandemic had been "appallingly difficult" and the government "acted throughout with the intention to save life... in accordance with the best scientific advice."

The testimony of Cummings, the brains behind the "Leave" campaign in the 2016 Brexit referendum, was much anticipated after he began attacking Johnson's coronavirus policies and financial dealings in recent weeks after quitting government in December.

During more than seven hours of testimony, he conceded "many, many institutions failed around the world" in their initial response to the crisis.

But he blasted senior UK officials and politicians for initially missing the seriousness of the situation, and once they did grasp it, of inept decision-making, comparing Johnson's approach to an out-of-control shopping trolley.

Cummings was blamed for undermining the government's coronavirus lockdown message by going on a trip with his family
Cummings was blamed for undermining the government's coronavirus lockdown message by going on a trip with his family AFP / Tolga AKMEN

Cummings said the Conservative leader initially branded coronavirus "a scare story", was consumed by issues in his private life and too reluctant to impose a lockdown in March 2020 because of the economic impact.

He said officials were guilty of "catastrophic" group-think, pursuing a haphazard strategy of so-called herd immunity before belatedly abandoning it when the likely death toll became clear.

Britain's top civil servant even suggested to Johnson in mid-March last year that he encourage "chickenpox" gatherings to spread infections and build immunity, according to Cummings.

Britain's successful Covid-19 vaccination campaign has boosted the government's approval ratings
Britain's successful Covid-19 vaccination campaign has boosted the government's approval ratings AFP / JUSTIN TALLIS

Comparing officials' eventual realisation of the situation to a scene in the movie "Independence Day" after an alien invasion, Cummings said the deputy cabinet secretary conceded to him that "there is no plan, we're in huge trouble".

Johnson grew more resistant to scientific advice, Cummings said, confirming media reports that the British leader said he would rather let "bodies pile high" than lock down again later in 2020.

"His argument was 'I should've been the mayor (in) 'Jaws' and kept the beaches open' -- that's what he said on many, many occasions," he said.

By the time Johnson did order another lockdown in late October, Cummings said their relationship had broken down. "I regarded him as unfit for the job," he added.

Cummings repeatedly singled out Health Secretary Matt Hancock for criticism, alleging he lied to colleagues on numerous occasions, including over pledges to test all elderly patients released from hospital back into care homes.

Hancock wanted scientists to take the blame for failings and could have been fired for "at least 15 or 20 things", Cummings alleged.

A spokesman for Hancock said "we absolutely reject" the claims and that he would "continue to work closely" with Johnson responding to the pandemic.

Cummings was appointed chief adviser by Johnson when he took power in July 2019, helping him to secure a thumping election victory that December.

The 49-year-old was criticised for undermining the government's lockdown message early in the pandemic when he went on a lengthy cross-country journey with his family.

During his evidence, Cummings said security concerns around his London home had been an additional, previously undisclosed, factor in the decision.

Despite Johnson riding high after successful local election results in England this month, Cummings' testimony could refocus attention on his government's patchy performance responding to the pandemic.

But Johnson's government has also overseen a successful vaccination drive, having offered more than two-thirds of adults at least one dose.