Helena Morrissey, a director at the Foreign Office, suggested the crisis has been exaggerated because people are not “dropping dead in the street”.
“The data shows we are NOT in a pandemic,” tweeted the peer, who was sent to the House of Lords by Boris Johnson last year.
“If people were dropping dead in the street we would notice & not go to M&S and have all those football matches.”
Baroness Morrissey then made claims about the role played by the Chinese Communist Party, adding: “CCP fake videos started this. It is ridiculous.”
The peer, a leading asset manager, is the senior non-executive director at the Foreign Office – a government role created to provide “strategic leadership” and “advice on performance and delivery”.
The controversy follows criticism of the failure to act when Tory MP Desmond Swayne said Covid statistics “appear to have been manipulated” and risks to the NHS were “manageable”.
“The prime minister must finally wake up to the threat of disinformation and conspiracy theories in his party’s ranks,” Ms Rayner said.
“He must take action against Conservative parliamentarians who undermine our national effort to defeat this virus and put more lives at risk by legitimising, promoting and endorsing deadly disinformation.”
The Covid-19 Bereaved Families for Justice group, which is campaigning for an independent inquiry into the pandemic response, called the comments “shocking” and “deeply upsetting”.
“We would urge Helena Morrissey to consider visiting the National Covid Memorial Wall opposite parliament, where palm-sized hearts for each of the lives lost to Covid-19 cover a wall half a kilometre in length,” it said.
Professor Christina Pagel, a member of the Independent Sage group of scientists, attacked “damaging ignorance”, saying: “It’s despicable. She is gaslighting the families of the 150,000 people who have died.”
And another member, Gabriel Scally, professor of public health at University of Bristol, said: “The pandemic indeed kills far more poor people and ethnic minority people than it does rich, white baronesses, but having a very public Covid-denier in a prominent governance role in the Foreign Office is surely unacceptable?”
Baroness Morrissey, who charges up to £20,000 for speaking engagements, also retweeted comments from the British rapper Zuby criticising the lockdown as “bulls***”.
It attacked shops, gyms and restaurants being closed while Americans were “going to nightclubs and throwing parties”, saying: “The UK is on some BS.”
Her comments on the Chinese ruling party’s alleged involvement in the pandemic come during increasing tension between Beijing and London.
The UK recently imposed sanctions on Chinese officials in response to the treatment of Uighur Muslims. The foreign secretary, Dominic Raab, has stopped short of labelling the situation a “genocide,” but has said it constitutes “appalling” human rights violations.
Downing Street declined to respond to calls for the prime minister to discipline the peer. Baroness Morrissey has also been approached for a response.