Sir Keir Starmer has accused Boris Johnson of “trying to shift the blame” for the Government’s coronavirus failings onto care homes after the Prime Minister suggested “too many” did not properly follow procedures.

The Labour leader said the PM had been “shameful” as the pair prepared to clash at Prime Minister’s Questions on Wednesday.

Mr Johnson’s comments were widely criticised and branded a “real slap in the face” for care workers by the Independent Care Group, while another sector leader said they were “clumsy and cowardly”.

On Tuesday evening, Sir Keir tweeted: “The Government’s own advice at the start of the pandemic said people in care homes were ‘very unlikely’ to be infected.

“Now Boris Johnson is trying to shift the blame.”

Earlier Downing Street declined to apologise and instead Mr Johnson’s official spokesman tried to clarify the comments.

“The Prime Minister was pointing out that nobody knew what the correct procedures were because the extent of asymptomatic transmission was not known at the time,” he said.

Press on whether Mr Johnson would like to apologise or retract the comments, the spokesman said: “As I’ve just set out, the PM thinks that throughout the pandemic care homes have done a brilliant job under very difficult circumstances.”

The Prime Minister’s remarks came after he was asked what he made of NHS chief executive Sir Simon Stevens’ desire to see plans to adequately fund the adult social care sector within a year.

Mr Johnson said: “One of the things the crisis has shown is we need to think about how we organise our social care package better and how we make sure we look after people better who are in social care.

“We discovered too many care homes didn’t really follow the procedures in the way that they could have but we’re learning lessons the whole time.”

But sector leaders said the suggestion that care home workers were not following procedures was “totally inappropriate” and “hugely insulting”.

Vic Rayner, executive director of the National Care Forum, told the BBC: “Care homes across the country were dealing with an extraordinary amount of different guidance that was coming out from Government on an almost daily basis.

“So for the suggestion that they were not following procedures as laid out is totally inappropriate and, frankly, hugely insulting.”

The Independent Care Group’s chairman Mike Padgham said it was “upsetting” for the PM to make such comments, and described them as “a real slap in the face for those workers after they have given and sacrificed so much”.

He said: “We hope he will reflect on those comments and see the incredible work the care sector has done in the recent months to care for older and vulnerable people, with late and conflicting advice and poor support in terms of personal protective equipment (PPE) and testing during this awful pandemic.

“And we hope it will spur him into long-promised action to reform the sector and end the crisis in social care which left us so vulnerable to a virus like Covid-19.”

Mark Adams, chief executive of the charity Community Integrated Care, said he was “unbelievably disappointed” to hear the Prime Minister blaming care workers.

He told BBC Radio 4’s Today programme: “I think this – at best – was clumsy and cowardly, but, to be honest with you, if this is genuinely his view, I think we’re almost entering a Kafkaesque alternative reality where the Government set the rules, we follow them, they don’t like the results and they then deny setting the rules and blame the people that were trying to do their best.

“It is hugely frustrating.”

A paper prepared by Public Health England on whether asymptomatic people with coronavirus are infectious, which was considered by the scientific advisory group for emergencies (Sage) on February 4, concluded that more data was needed to determine whether transmission can occur from asymptomatic individuals.

But until March 13, care home guidance said that for care staff visiting patients at home or providing care to residents there “is no need to change your approach” if the person they are visiting is asymptomatic.

Guidance for symptomatic patients stated staff should “avoid any further physical contact with the person”.

The row comes as Chancellor Rishi Sunak prepares to deliver his economic update on how to recover from the coronavirus crisis on Wednesday.

Among his plans, he will unveil a £3 billion green package with grants for homeowners and public buildings to improve energy efficiency as part of his coronavirus economic strategy.

Mr Sunak will set out a raft of measures in his Commons statement on Wednesday, including £2 billion for households to insulate their homes and make them more energy-efficient.

The funding aims to help the UK “build back greener” and meet its legally binding target to cut greenhouse gas emissions to net zero by 2050, but campaigners say it “doesn’t measure up to the economic and environmental crises”.