Coronavirus could already have infected HALF the British population and has been spreading in the UK since January, a new study claims.

Oxford University researchers say the deadly bug is thought to have been circulating around a month before the first reported case and six weeks before the first reported death.

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3 Experts say coronavirus could already have infected half the British population Credit: Getty Images - Getty

This means it could have had enough time to have spread widely - with many individuals developing immunity, experts warned.

It reinforces the call for better testing in the UK - to identify those people who have already been infected, and are now immune.

Yesterday, Health Secretary Matt Hancock announced 3.5 million of these antibody tests have been bought by the government, and should be available in days to weeks.

Sunetra Gupta, a professor of theoretical epidemiology who led the new study, said testing was needed to assess the new theory.

She said: "We need immediately to begin large-scale serological surveys – antibody testing – to assess what stage of the epidemic we are in now."

The study from Oxford’s Evolutionary Ecology of Infectious Disease group suggests that Covid-19 reached the UK by mid-January at the latest.

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Like many emerging infections, it spread invisibly for more than a month before the first transmissions within the UK were officially recorded at the end of February.

The Oxford study is based on a what is known as a “susceptibility-infected-recovered model” of Covid-19, built up from case and death reports from the UK and Italy.

The researchers say they made what they believe are the most plausible assumptions about the behaviour of the virus.

The modelling brings back into focus “herd immunity”, the idea that the virus will stop spreading when enough people have become resistant to it because they have already been infected - whether they were aware of it or not.

The government last week abandoned its unofficial herd immunity strategy — allowing controlled spread of infection — after its scientific advisers said this would put the NHS under immense strain with critically ill patients.

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Despite this, the Oxford results would suggest the country had already gained substantial herd immunity through the unrecognised spread of Covid-19 over more than two months.

If the findings are confirmed by testing, then the current restrictions on travel and socialising could be removed much sooner than ministers have indicated.

To provide the necessary evidence, the Oxford group is working with colleagues at the Universities of Cambridge and Kent to start antibody testing on the general population as soon as possible.

Just yesterday, the Health Secretary announced that 3.5 million antibody tests had been bought - which will show if you have had Covid-19.

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Speaking at Downing Street, he said: "We've now bought 3.5 million antibody tests that will allow people to see whether they have had the virus and are immune to it and then can get back to work.

"We expect people not to be able to catch it, except in very exceptional circumstances, for a second time."

He added that a new testing facility in Milton Keynes opened yesterday to process the checks ahead of them being ramped up.

The UK yesterday saw its biggest daily spike in deaths from coronavirus, taking the nationwide total to 424.

Eighty-three of the 89 coronavirus fatalities confirmed on Tuesday were in England, with two in Scotland, one in Wales, and three in Northern Ireland.

On top of this, 1,427 more patients were confirmed to have the virus - taking the total number of infected Brits to over 8,000.

However, the true size of the outbreak is likely unknown because of the Government's controversial decision to only test patients in hospital.

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