Analysis carried out by the group Hope Not Hate claims that between 16 and 22 per cent of the population believe in baseless claims about the virus outbreak, including that it had been orchestrated to control the population.
The campaign group has also said that the UK is currently "the most significant country" for support for conspiracy group QAnon outside the US.
In its annual State of Hate report published today (Monday), which provides a detailed overview of the current state of extremism, nationalism, racism and misinformation, it warned that the "groundswell of anxiety" caused by the crisis has fed a "constellation" of organisations and theorists such as the anti-vaxx movement.
The report says: "From March onwards we saw meteoric increases in engagement with conspiracy content online, from anti-vaccine to anti-5G content, as well as QAnon pages and groups.
"Hope Not Hate’s polling repeatedly found alarming awareness of conspiracy theories among the British public."
As many as 40 per cent of 1,492 people polled said they had been exposed to claims that Covid-19 was being spread as a "bio-weapon" by the Chinese state, while more than a third (35 per cent) said they had come across material claiming the pandemic was part of a "depopulation plan" orchestrated by the UN or New World Order.
Although only a small percentage of people said they believed in the theories, the levels are "worryingly high", the report said.
Some four per cent of people also said they believed it was "definitely true" that the Covid-19 vaccine was being used to "maliciously infect people with poison", and a further 11 per cent said this was "probably true".
The report also draws parallels between conspiracy theorists spreading unverified claims about coronavirus and the lockdown with the far-right scene, with figures such as former BNP leader Nick Griffin and far-right influencer Paul Joseph Watson having used the pandemic to spread anti-Semitic or Islamophobic messages.
Chinese people have also increasingly been victims of hate crimes over the past year, with the report saying anti-Chinese rhetoric was "encouraged" by President Donald Trump before his defeat in the US elections last year.
Nick Lowles, CEO of Hope Not Hate, said the pandemic and lockdown had proved to be "a fertile time" for conspiracy theorists, many of whom had created confusion and fear over 5G technology, supposed celebrity child abuse networks and the safety of vaccines.
Mr Lowles said: "Although some of these narratives are merely outlandish, they often cohabit space with conspiracies infused with antisemitic tropes and risk being a transmission mechanism for anti-Jewish sentiment to the unsuspecting.
"Social media has been the oxygen for these obscure ideas, and though tech giants have begun to remove the most notorious, they are proving a stubborn weed to root out.
"Whilst we need more assertive action on this front, that will not solve the underlying issues of distrust and fear that drive people to search for answers in these ideas."
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