Matt Hancock has denied promising Boris Johnson in March 2020 that all patients discharged from hospitals into care homes were being tested for Covid-19 before transfer.

The supposed pledge was a central plank of Dominic Cummings’s scathing attack on the health secretary, who was accused by the prime minister’s former top adviser of repeatedly lying about the protections being put in place to shield the vulnerable, with the result that “tens of thousands of people died who didn’t need to die”.

In explosive testimony given over seven hours to a House of Commons inquiry, Cummings said that Hancock had given the PM “categorical” assurances – which turned out to be untrue – that patients entering care homes would be tested. The health secretary’s claims to have thrown a protective shield around the sector were “complete nonsense”, he said.

But Mr Hancock insisted that he had only ever committed to delivering testing for people going into care homes “when we could do it”, and said that the process of building a testing system took time. He said that his target of reaching 100,000 tests by the end of April had been “very effective” in meeting the goal – even though Cummings on Wednesday said it had disrupted the operation, blasting it as “incredibly stupid… criminal, disgraceful”.

Mr Hancock’s defence came as Mr Johnson sought to evade his former right-hand man’s brutal assessment of him as “unfit to govern”, telling reporters: “I think, if I may say so, that some of the commentary I have heard doesn’t bear any relation to reality.” He dodged the question of whether he had said that he was ready to see “bodies pile high” rather than order another lockdown.

And Cabinet Office minister Michael Gove, asked by a Commons committee if Mr Cummings was right to say his department had been “terrifyingly s**t”, with “no plans”, and “totally behind the pace”, replied simply: “No.”

As Mr Hancock’s career hung in the balance in the wake of the former Vote Leave supremo’s onslaught, there were calls for an immediate inquiry into the wave of deaths which coronavirus brought to care homes last year.

Coronavirus was mentioned on the death certificates of more than 35,000 care home residents in England and Wales between the onset of the pandemic in March 2020 and February this year. As many as 25,000 elderly people are believed to have been discharged into homes without tests, largely during the early weeks of the emergency, as hospitals sought to clear beds for the expected influx of patients needing intensive care.

The impact of the transfers can be seen in the fact that the 19,286 Covid-related deaths recorded in care homes between March and June 2020 made up around 40 per cent of the national total for that period, compared to the 16,355 recorded between October and February, which accounted for only 26 per cent of deaths in the second wave.

Former Conservative health minister and NHS doctor Dan Poulter, vice chair of the all-party parliamentary group for coronavirus, said: “There is a strong case for conducting an immediate inquiry into Covid-related deaths in care homes. This would help ensure lessons are learnt so that care homes are better protected ahead of any third wave.

“It is one of the most troubling aspects of this pandemic that the elderly have borne the brunt despite being the most vulnerable in society. We must ensure these mistakes are not repeated and that care homes are never again treated as an afterthought in pandemic planning.”

And Helen Keenan, whose mother Kathleen died in a care home from coronavirus after being transferred from hospital, said: “I would like to see the statutory public inquiry brought forward, because waiting until 2022 is frankly insulting to the people who have lost loved ones. There is no excuse for leaving it any longer.”

The Bereaved Families for Justice group said: “This political pantomime continues to show a level of disrespect to our lost loved ones and brings us no closer to the answers we need for lives to be saved. If the government have time to play a leading role in this sideshow they have the time to get on with an inquiry.”

Labour leader Sir Keir Starmer stressed that Mr Johnson, as prime minister, was ultimately responsible for failings in the UK’s response to coronavirus.

Speaking during a visit to Bristol, Starmer said: “What we need to do is put what Dominic Cummings said alongside the facts we know. We’ve got one of the highest death tolls in Europe and the families who have lost someone are entitled to answers in relation to this. Bad decisions have consequences. In this case, I’m afraid, they’re unnecessary deaths.

“They’re very, very serious allegations. They paint a picture that actually leads to the prime minister – the buck stops with him.”

Less than 24 hours after Cummings’s bruising assault on him, Mr Hancock appeared before MPs for an hour of questioning in the Commons, where he insisted that “these unsubstantiated allegations around honesty are not true” and said he had been “straight with people in public and in private throughout”.

But his failure to address Cummings’s core allegations directly was condemned as “extremely disrespectful to those who have died and their loved ones” by shadow health secretary Jonathan Ashworth.

Speaking later at a Downing Street press conference, the health secretary was repeatedly pressed by reporters to spell out whether he had in fact given the PM a “categorical” assurance that patients going into homes were being tested.

He replied: “No. There will be a time when we go back over all this in great detail, but my recollection of events is that I committed to delivering testing for people going into care homes when we could do it.

“I committed to getting the policy in place, but it took time to build the testing capacity.”

Asked why tests before discharge for care home residents did not become national policy until mid-April – a month after it was introduced locally in some areas – he replied: “Unfortunately we didn’t have the testing capacity to put that policy in place across the whole country.

“It would have been wonderful if we’d started this pandemic with a very large testing capacity. We didn’t. We had to build one.”

Speaking during a visit to a hospital in Essex, Mr Johnson described care home deaths as “tragic”, but insisted: “We did everything we could to protect the NHS and to protect care homes as well.”

But the general secretary of public sector union Unison, Christina McAnea, retorted: “It’s simply not true the government did all it could to protect the care sector.

“Discharging hospital patients into care homes without testing was a colossal mistake that could and should have been avoided. It’s just one of many ways that the government has failed care staff, residents and their families.”