Dominic Cummings ramped up his attacks on Boris Johnson on the eve of the former aide’s evidence session, accusing the prime minister of having no “serious plan” to protect society’s most vulnerable people from Covid. Johnson – along with ministers, government scientific advisers and civil servants – is braced for a lambasting from the man who was his most senior adviser until November, when Cummings is questioned by MPs on Wednesday. It has been reported Cummings will use his appearance before MPs to claim Johnson referred to coronavirus as “kung-flu”, and was willing to be infected with the virus live on TV – a statement that was allegedly made before he contracted the disease. Downing Street did not deny the claim. A No 10 spokesperson said: “We are entirely focused on recovering from the pandemic, moving through the roadmap and distributing vaccines while delivering on the public’s priorities.” Cummings is expected to blame those around him for failings in the handling of the pandemic in February and March last year, and in September when Johnson rejected a “circuit-breaker” lockdown. “Throughout this pandemic, the government’s priority has been to save lives, protect the NHS and support people’s jobs and livelihoods across the United Kingdom.” On Tuesday, Cummings added to a 63-tweet thread on Twitter, saying that those in care homes and other social care, and vulnerable people asked to shield, had been failed. “One of the worst failings in Feb/March, less discussed than lockdown, was the almost total absence of a serious plan for shielding/social care,” he claimed. “As in general, there was widespread delusion we HAD a great plan. It turned out to barely exist.” He said a helpline number was left off letters to members of the public being asked to shield from the virus because the helpline had not yet been set up. Cummings is to allege that, when Johnson rejected the argument for a September lockdown, he claimed “Covid is only killing 80-year-olds”, according to ITV’s political editor Robert Peston. The former aide will also be questioned on allegations – denied by No 10 – that Johnson said he would rather “let the bodies pile high in their thousands” than impose another lockdown. The failure to properly protect care home residents, with many discharged from hospital back into care settings where the virus then spread, is regarded as a key mistake of the early days of the pandemic. This month the Guardian revealed that more people died with Covid in care homes in England and Wales in the second wave of the pandemic than in the first. In total, more than 40,000 had Covid mentioned on their death certificate since March 2020. Angela Rayner, Labour’s deputy leader, said Johnson’s comments about Covid “only killing 80-year-olds” was “utterly disgraceful”. “The prime minister has once again shown a shameful disregard for other people’s lives.” Cummings will be questioned by the House of Commons science and technology committees for several hours as part of their inquiry into the government’s handling of the pandemic. He has also promised to hand over relevant documents. According to a statement from the committees, they plan to cover “the government’s preparedness; decision-making in the early months of the pandemic; the level of scientific evidence available to the government; its border policy; and the effectiveness of its public health messaging and communications”. Johnson loyalists on the panel may also seek to discredit the prime minister’s former aide, whom friends say remains hurt by his abrupt departure from the centre of power and wants revenge on his former boss. Cummings has previously dubbed the government’s border policy a “joke” and described the Department of Health as a “smoking ruin”.Government insiders are infuriated by the drip, drip of accusations from the former adviser, whom many believe damaged the credibility of the government with his trip to Durham during lockdown – and who they point out was involved in making many of the decisions he is now criticising. Former Brexit secretary David Davis said Cummings may have correctly identified some of the government’s failings – but there was little evidence he had tried to correct them when he was inside government. “This is a man whose primary purpose in life is to rewrite history to make him look good, but that doesn’t mean that everything he says is completely wrong,” he said. Wednesday’s session will be chaired by two Conservative former cabinet ministers, Jeremy Hunt and Greg Clark, chairs of the cross-party health and science select committees respectively. Over the weekend, Cummings argued that a fundamental problem with the government’s approach to the early days of the pandemic was the pre-existing plan for tackling a flu-like virus, which pointed to the impossibility of stopping its spread. Instead, Cummings claims the central plan initially was to rely on building up herd immunity, as more people caught the disease – until modelling showed that would involve an unmanageable death toll and put impossible pressure on the NHS. Downing Street adamantly denies that herd immunity was ever the aim of government policy, though it was mooted by chief scientific adviser Patrick Vallance. On 13 March last year, Vallance said: “Our aim is to try and reduce the peak, broaden the peak, not suppress it completely; also, because the vast majority of people get a mild illness, to build up some kind of herd immunity so more people are immune to this disease and we reduce the transmission, at the same time we protect those who are most vulnerable to it.” Other contentious issues expected to be aired at the hearing include whether Johnson devoted sufficient time to focusing on the pandemic in its early days, amid allegations – also denied by No 10 – that he was also trying to finish a long-promised book on Shakespeare. Cummings fell out with Johnson and left Downing Street in November alongside the prime minister’s then director of communications, Lee Cain. No 10 has since accused Cummings of being involved in a series of damaging leaks, something he has denied. So intense is the speculation at Westminster about the impact of the hearing that Downing Street was forced to deny last week that Johnson is planning a cabinet reshuffle in order to detract from Cummings’ intervention. The announcement at the weekend that Johnson will marry his partner, Carrie Symonds – though not until July 2022 – was also widely regarded as an attempt to detract attention from the Cummings hearing. The evidence session is due to start at 9.30am and is expected to be ongoing on Wednesday when Johnson has to face the Labour leader, Keir Starmer, at prime minister’s questions, at noon.