Coronavirus was in the UK weeks before the first acknowledged cases, according to fresh analysis on the outbreak.
And there were multiple 'patient zeros' which quickly spread the virus scientists believe.
A new genetic analysis of coronavirus, which causes Covid-19, taken from more than 7,600 patients worldwide shows it has been circulating since late last year when it first emerged from Wuhan in China.
Researchers in the UK have been studying mutations in the virus and found evidence of how quickly it spread - but no evidence that it is becoming easier to spread or deadlier.
Francois Balloux of the University College London Genetics Institute told CNN it will be impossible to find the "first" patient in any country.
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"All these ideas about trying to find a Patient Zero are pointless because there are so many patient zeros," he said.
He added: "The virus is changing, but this in itself does not mean it's getting worse."
His team looked at samples of the virus taken at different times and from different places which they say indicates the virus started infecting people at the end of last year.
Their report, published in the journal Infection, Genetics and Evoltion says that: "This rules out any scenario that assumes SARSCoV-2 may have been in circulation long before it was identified, and hence have already infected large proportions of the population."
The analysis shows a 'common ancestor' for the virus - likely a bat - but there have since been multiple mutations.
Viral samples taken from all corners of the globe show multiple mutations, and they are similar mutations.
"Everything is everywhere," the team wrote. "It has been introduced and introduced and introduced in almost all countries," Mr Balloux added.
"All viruses naturally mutate. Mutations in themselves are not a bad thing and there is nothing to suggest SARS-CoV-2 is mutating faster or slower than expected.
"So far we cannot say whether SARS-CoV-2 is becoming more or less lethal and contagious," Mr Balloux said.
Balloux's team's findings were reviewed by other experts, a process called peer review, before they were published in the journal.
Today Prime Minister Boris Johnson set the UK a target of conducting 200,000 coronavirus tests a day in a bid to try and 'reopen' the country and the economy.
The 200,000 daily testing capacity could include new antibody tests if any are found to work accurately, Downing Street said.
"What it will ensure is that we have the capacity to provide tests to asymptomatic people, in hospitals and in other sectors, and also it will ensure that we have the capacity we need once the test, track and trace programme is up and running," the Prime Minister's official spokesman said.
The target covers all available testing pillars "and also would include antibody tests if and when we can find a test which we are confident is accurate".
The number of tests actually carried out will be guided by clinical advice, the spokesman said.
