“Disastrous” mistakes by Boris Johnson’s government caused tens of thousands of unnecessary deaths, the prime minister’s former top adviser has told MPs.

Mr Cummings said Mr Johnson locked England down at least three weeks late in the spring of 2020, as the government pursued a “herd immunity” strategy in the hope of limiting the disease to a single peak by letting people catch the virus.

He accused the PM of ignoring advice to call a second “circuit-breaker” lockdown in the autumn, confirming that he heard Johnson say he would rather “see bodies pile high” than shut down the economy again.

And he launched a sustained attack on the “criminal, disgraceful” actions of health secretaryMatt Hancock, who he said should have been sacked 20 times over for lying about the availability of personal protection equipment (PPE) and the testing of hospital patients discharged into care homes.

Giving evidence to an inquiry by the House of Commons health and science committees, Mr Cummings said that many of the failings behind the UK’s huge death toll remain in place, including inadequate control of borders.

And he said there was “no excuse” for the PM to delay a public inquiry into the handling of the pandemic until next year. MPs should make clear that the proposed timetable is “intolerable”, he said.

“Tens of thousands of people died who didn’t need to die,” said Mr Cummings. “There’s absolutely no excuse for delaying that. A lot of the reasons for why that happened are still in place.”

Mr Cummings said Johnson and other government leaders were “completely out of their depth” when coronavirus hit. He described the PM as “like a shopping trolley smashing from one side of the aisle to another”.

He portrayed a “lack of urgency” in 10 Downing Street, with the prime minister treating Covid-19 as a “scare story” and officials suggesting that herd immunity could be achieved by encouraging people to hold “chickenpox parties”.

Mr Johnson even suggested he could have himself injected with the virus on live TV to convince people it was safe, he said.

Cummings accused Mr Hancock of using chief medical officer Chris Whitty and chief scientific adviser as “a shield for himself”, repeatedy declaring he was following the science in order to be able to blame them if things went wrong.

Mr Cummings said he advised Mr Johnson against the reopening of the economy in the summer of 2020, arguing unsuccessfully against calls for workers to return to offices and the return of students to universities in September.

When the second wave of coronavirus arrived in the autumn, he said that Mr Johnson wanted to be like “the mayor in Jaws”, who notoriously kept beaches open despite shark attacks.

Cummings described as “completely mad” Johnson’s decision to reject scientific advice for a two-week lockdown in September. Despite “all credible, serious people” arguing for the shutdown to nip a second wave in the bud, Mr Johnson decided he was “just going to ignore the advice”, he said.

And he confirmed he heard Mr Johnson say in October that he would rather see “bodies pile high” than impose another lockdown on the nation.

“I heard that in the prime minister’s study,” said Cummings. “That was not in September though, that was immediately after he finally made the decision to do the lockdown on 31 October.”

Explaining his decision to resign in November, he said that his relationship with Johnson had taken a “terrible dive” because the PM knew that “I blamed him for the whole situation”.

“Fundamentally, I regarded him as unfit for the job,” said Mr Cummings, who added that Mr Johnson’s fiancee Carrie Symonds was “trying to appoint her friends to particular jobs” in Downing Street.

He said that he now felt he should have gone to the PM in September and “held the gun to his head” by threatening to resign unless he ordered a second lockdown.

“If I had gambled then and said ‘I will basically call a press conference, and blow this thing sky high’ and then he had caved in and done it, tens of thousands of people would now still be alive,” said Mr Cummings.

“And we could have avoided the whole horror of the delays and the variants and Christmas and the nightmare that the country’s gone through in the first quarter of this year. I think I made the wrong decision and I apologise for that.”

Mr Cummings defended his own decision to take his family to Durham at the height of the first wave, despite admitting the fallout from the trip was “a major disaster for the government and the Covid policy”.

He said it was “bizarre” that ministers were now denying that herd immunity was the government’s plan until mid-March last year.

He said this led to delays in the closure of borders and the introduction of face-coverings and mass testing as the public health administration accepted “ludicrous” beliefs that these measures would be ineffective, he said.

At the time, Mr Johnson was “going through a very, very difficult time in his private life”, with his divorce and pressure from Carrie to announce her pregnancy and their engagement, as well as “his finances and all that stuff”, he said.

The former Vote Leave supremo admitted he was “frightened” to challenge the “groupthink” from Whitehall departments and scientific advisers that herd immunity would avoid a second wave of virus in the winter, when the NHS would be under pressure from seasonal illnesses.

He told MPs that he “hit the panic button” on 11 March after being told by independent scientists that the plan was “completely flawed” and that the UK was heading for its worst catastrophe since World War 2 with up to 500,000 dead.

But he said that even this was “far, far too late”, telling MPs: “I failed and I apologise for that.”

Mr Cummings told MPs that if the PM had refused to change course at this point, he was considering resigning and issuing a public warning that the government was “going to kill hundreds of thousands of people”.

Even after the switch to a lockdown policy, he said there was no plan in place for shielding vulnerable people, testing for the virus or for providing furlough payments to those who were unable to work.

And he described a “meltdown weekend” in late March after Mr Johnson himself caught Covid-19 and went into infectious care, when he said that “in many ways, the whole core of government fell apart”.

“There is no doubt that the prime minister made some very bad misjudgments and got some very serious things wrong,” said Mr Cummings. “It’s also the case that there’s no doubt that he was extremely badly let down by the whole system. It’s a system failure, of which I include myself in that as well. I also failed.”

There was “no doubt that many senior people performed disastrously below the standards which the country has a right to expect”, he said.

He accused Mr Hancock of “lying to everybody on multiple occasions” in official meetings and in public, and said that both he and cabinet secretary Mark Sedwill repeatedly urged Mr Johnson to sack him.

Sir Mark told the PM he had “lost confidence in the secretary of state’s honesty” and warned that “the British system is not set up to deal with a Secretary of State who repeatedly lies in meetings”, said Mr Cummings. And he said he himself warned that if Hancock remained in post “we are going to kill people and it will be a catastrophe”.

He said that Mr Johnson “came close” to removing the health secretary in April 2020, but “just fundamentally wouldn’t do it”, adding: “There was certainly no good reason for keeping him.”

When the health secretary was claiming that everyone was getting the treatment they needed in the first wave, many were in fact “dying in horrific circumstances”, he said. And he said that Mr Hancock had wrongly assured the PM that there was no problem with supplies of personal protective equipment (PPE) and later wrongly blamed the Treasury for shortages.

Mr Cummings said Mr Hancock – who will himself give evidence to the committees on 10 June – should have been fired for his “incredibly stupid” public commitment to 100,000 tests a day by the end of April 2020, which had diverted resources and “completely disrupted” the programme.

“It was criminal, disgraceful behaviour which caused serious harm,” he said, saying that this was the reason testing was taken away from the Department of Health and put into a separate agency.

And he said that Mr Hancock gave “categorical” assurances in March 2020 that people were being tested for Covid-19 before being discharged from hospital into care homes, when “we subsequently found out that that hadn’t happened”. Government rhetoric about “putting a shield around care homes” was “complete nonsense”, he said.

The release of elderly patients to care homes “wasn’t thought through properly, there wasn’t any kind of proper plan”.

“It’s clear in retrospect that a completely catastrophic situation happened with these people being sent back untested and seeding coronavirus in care homes,” he said. “It was a function of the fact that the system was completely overwhelmed.”

And he told MPs: “We were told that people wouldn’t be sent back to care homes until after they’ve been tested for Covid and we were told that there was a plan for shielding. It turned out that neither of those things was correct.

“We didn’t really understand the catastrophe around people being sent back to care homes who were already Covid-infected until April.”

Mr Cummings praised chief scientific adviser Sir Patrick Vallance for proposing a vaccine taskforce under Katie Bingham to drive the jabs programme outside the Whitehall system.

But he said it was now “obvious” that at the outset of the pandemic, when pharmaceutical companies developed potential vaccines “literally within hours”, the government should have set up immediate human trials.

By paying human guinea-pigs to be inoculated with experimental vaccines and infected with Covid, the UK could have brought forward the first immunisations from December to September, he said.

Looking back to the process which led to the imposition of lockdown in the UK on 23 March, Mr Cummings said: “In retrospect, it’s clear that the official plan was wrong, it’s clear that the whole advice was wrong and I think it’s clear that we obviously should have locked down essentially in the first week of March at the latest.”

Assurances given by Mr Hancock in January last year that effective pandemic preparations were in place “were basically completely hollow”.

In an ideal world, he said the Covid response would have been led by “a kind of dictator… with close to kingly authority”, naming his preferred candidate as Marc Warner – a data specialist who worked with him on the Vote Leave campaign and whose scientist brother Ben was controversially drafted into government meetings on the pandemic.

He hailed Marc Warner, the chief executive of artificial intelligence company Faculty, as “one of the smartest and most ethical people I’ve ever met” and said that he had personally saved thousands of lives by raising the alarm about the herd immunity strategy after being drafted into the Covid operation by NHS England boss Simon Stevens.

Ideally, the UK would have introduced Taiwan-style mass testing, closed borders and compulsory quarantine from January, with individual and household isolation for those infected the following month, said Cummings.

But he said that the PM and many other senior people in Whitehall had the view that the economic danger from lockdown was worse than the health threat from coronavirus. Their assumption was that the British public would not accept lockdowns of the kind seen in China, he said.

At one meeting on 12 March he said that Sir Mark Sedwill told Mr Johnson: “Prime minister you should go on TV tomorrow and explain to people the herd immunity plan and that it’s like the old chickenpox parties, we need people to get this disease because that’s how we get herd immunity by September.”

“There were quite a few people around Whitehall who thought that the real danger was to the economy,” Mr Cummings told MPs.

“The prime minister’s view throughout January, February, March was – as he said in many meetings – the real danger here is not disease, the real danger is the measures that we take to deal with the disease and the economic destruction that that will cause.”

He blamed “groupthink” at the highest levels of government for the failure to raise the alert about the possible scale of the threat from coronavirus. But he rejected suggestions that chancellor Rishi Sunak was among those attempting to prevent lockdown, insisting he had been “supportive” throughout.

Mr Cummings said the response was hobbled by the inadequacies of the data provided to government.

“The lack of testing data was an absolutely critical disaster because we didn’t realise early enough how far it had already spread,” he told MPs.

“The testing data was wrong, the graphs we were shown and the models were all wrong because they were all pushed out to the right, and that massively contributed to the whole lack of urgency.”

Mr Cummings said that he realised that the logic behind the UK’s approach was “completely flawed”, after being approached in early March by a scientist who warned that the plan “could easily be mad… could be incredibly destructive”.

He said he raised concerns with members of the PM’s Scientific Advisory Group (Sage) the evening of 11 March.

And he said he sent a message to Johnson the following morning warning that the government approach was “completely behind the pace” and that the public must be advised immediately to stay at home in order to avoid as many as 500,000 deaths.

The scale of the trauma which he envisaged was reflected in a line scribbled in marker pen on the bottom of a whiteboard sketching out the first draft of Plan B on 12 March, which asked: “Who do we NOT save?”

He said “enormous credit” should go to the government’s second most senior civil servant Helen McNamara, who marched into 10 Downing Street on 13 March to tell the PM that on the basis of what experts had told her: “There is no plan. We are in huge trouble… I think we are absolutely f***ked.”

The situation in Downing Street in mid-March was like “a scene from Independence Day with Jeff Goldblum saying the aliens are here and your whole plan is broken and you need a new plan”, said Mr Cummings.

At a crucial meeting on March 14 Boris Johnson was told that models showing the peak was “weeks and weeks and weeks away” in June were “completely wrong” and that the government had to “gamble on an alternative plan”.

He said the PM was warned: “The NHS is going to be smashed in weeks, really we’ve got days to act.”

Mr Cummings admitted: “The truth is that senior ministers senior officials, senior advisors like me fell disastrously short of the standards the public has a right to expect of its government in a crisis like this,” said Mr Cummings.

“When the public needed it most, the government failed. And I like to say to all the families of those who died unnecessarily how sorry I am for the mistakes that were made and for my own mistakes at that.”

He admitted that he had delayed challenging the herd immunity policy because he was “frightened” of standing up against the prevailing consensus from Sage, the Department of Health and the Cabinet Office that trying to suppress Covid in the spring would simply lead to a worse outbreak when restrictions were eventually lifted later in the year.

“I was asking myself in that two-week period, if I pull if I hit the panic button and persuade the prime minister to shift and then it all goes completely wrong, I’m going to have killed God knows how many hundreds of thousands of people,” he said.

“If I’d acted earlier, lots of people might still be alive.”

He denied that the government’s failings were down to poor communications, instead blaming Mr Johnson’s failure to make his mind up.

“Fundamentally, the reason for all these problems was bad policy decisions, bad planning, bad operational capability,” he said.

“It doesn’t matter if you’ve got great people doing communications, if the prime minister changes his mind 10 times a day and then calls up the media and contradicts his own policy, day after day after day, you’re going to have a communications disaster.”

Mr Cummings said the government had failed to explain to the public the importance of self-isolation for those who may have come into contact with Covid and failed to provide proper incentives for them to comply.

He said he argued for a South Korean-style “carrot and stick” system of financial support backed up with the threat of jail for breaking quarantine.

“If we had just cut-and-pasted what they were doing in Singapore or Taiwan, everything would have been better,” he told MPs.

Mr Cummings said: “Fundamentally, there was no proper border policy because the Prime Minister never wanted a proper border policy.

“Repeatedly in meeting after meeting I and others said all we have to do is download the Singapore or Taiwan documents in English and impose them here.

“We’re imposing all of these restrictions on people domestically but people can see that everyone is coming in from infected areas, it’s madness, it’s undermining the whole message that we should take it seriously.

“At that point he was back to, ‘lockdown was all a terrible mistake, I should’ve been the mayor of Jaws, we should never have done lockdown one, the travel industry will all be destroyed if we bring in a serious border policy’.

“To which, of course, some of us said there’s not going to be a tourism industry in the autumn if we have a second wave, the whole logic was completely wrong.”

He told MPs that he probably should have resigned in September 2020, because of the fundamental differences between himself and the PM on Covid policy.

“If I could have clicked my fingers and done things, there would have been a serious border policy, masks would have been compulsory, Hancock would have been fired, we’d have done dozens and dozens and dozens of things,” he said.

“Fundamentally, the prime minister and I did not agree about Covid after March. After March, he thought the lesson to be learned, is we shouldn’t have been locked down, we should have focused on the economy, it was all a disaster, he should have been the mayor in Jaws. I thought that perspective was completely mad.”

Mr Cummings said that many junior officials had performed well in the pandemic, only to be let down by the failings of their leaders.

He told MPs: “It’s just completely crackers that someone like me should have been in there, just the same as it’s crackers that Boris Johnson was in there, and that the choice at the last election was Jeremy Corbyn.

“The problem in this crisis was very much ‘lions led by donkeys’ over and over again.”

Describing the atmosphere within government in the crucial weeks when Covid-19 was spreading from China to Europe, Mr Cummings said: “No 10 was not operating on a war footing in February in any way shape or form. Lots of key people were literally skiing.

Mr Cummings said: “In February the prime minister regarded this as just a scare story, he described it as the new swine flu.”

Asked if he had told Johnson this was not the case, he told MPs: “Certainly, but the view of various officials inside Number 10 was if we have the Prime Minister chairing Cobra meetings and he just tells everyone ‘it’s swine flu, don’t worry about it, I’m going to get (chief medical officer) Chris Whitty to inject me live on TV with coronavirus so everyone realises it’s nothing to be frightened of’, that would not help actually serious panic.”