Four of the British evacuees who landed back in Britain from Japan on Saturday have tested positive for COVID-19, taking the number of UK cases to 13.
The virus was transmitted when they were on the Diamond Princess cruise ship.
They are being transferred from Arrowe Park Hospital in Wirral to specialist NHS infection centres, England's chief medical officer, Professor Chris Whitty, said.
It has also emerged that while they were tested in Japan, the results did not come back until Sunday, meaning it was unclear whether they were infected when they boarded the plane back to the UK.
The Department of Health said the new cases were confirmed following "test results received from Japan".
It added that a "full infectious disease risk assessment" was carried out, and no one who boarded the repatriation flight displayed any symptoms.
It previously said that all the evacuees tested negative before getting on the plane.
Sky News correspondent Sally Lockwood, who has seen WhatsApp messages shared between the evacuees, said there was "mounting anger" following the confirmation of the new cases.
One text said: "We were told that no one would be on the flight unless they tested negative - that obviously isn't the case."
In another one, an evacuee wrote: "They let them fly without the results, so they have put us in a position where we now could have it too."
Paul Hunter, professor of health protection at the University of East Anglia, was highly critical of the error.
"How anybody would think that you could actually take samples from people to make sure they're not positive and then put them on a plane to tell them a few days later is indefensible," he told Sky News.
But Keith Neal, professor of epidemiology of infectious diseases at the University of Nottingham, said quarantine on the Diamond Princess was not working and the British passengers needed to be evacuated.
Almost a fifth of the 3,711 holidaymakers originally on board have been infected.
"The UK authorities brought the passengers home as they would have continued to be at risk staying on the ship," Professor Neal said.
Those remaining at Arrowe Park will be quarantined for two weeks, having already spent 14 days in isolation on the ship.
The Department of Health said "appropriate arrangements" were in place at Arrowe Park, including strict separation of passengers from staff and from each other.
Thirty Britons and two Irish citizens landed at Boscombe Down Ministry of Defence base near Salisbury, Wiltshire, before being taken to hospital by coach on Saturday.
Meanwhile, there has been a third fatality from the COVID-19 outbreak on the Diamond Princess.
Japan's health ministry said a passenger who was taken to hospital after testing positive had died.
The Japanese man in his eighties was among the first group of people to develop symptoms when the ship was put under a 14-day quarantine on 5 February, health ministry official Masami Sakoi said.
A total of four people have died from the virus in Japan - all of them in their 80s.
In Italy, about a dozen towns are in lockdown as the country races to contain the biggest outbreak of coronavirus in Europe following a surge in cases.
The number has risen sharply to more than 150, and three people have died in the last 48 hours.
Elsewhere, South Korea has declared its highest disease alert level as it reported more than 160 new coronavirus cases, bringing the total there to 763.
In another development, more than 100 people flown back to the UK from the epicentre of the coronavirus outbreak in China have been released from quarantine.
The group - including 10 children and a family of four - spent two weeks at a conference centre in Milton Keynes after being brought back to Britain on a repatriation flight from the city of Wuhan.