UK health officials are hunting for a mystery Covid-19 patient infected with the variant of the virus that was identified in Brazil.
It is one of six cases of the “variant of concern” identified in the UK in February.
Three cases were identified in Scotland and two in South Gloucestershire, near Bristol in England.
But officials do not know who one of the cases is, or where they were tested.
A public appeal is under way to find the person and track down hundreds of other passengers who arrived in the UK by connecting flights from Brazil last month.
Anyone tested for coronavirus on February 12 or 13 and did not get the result is asked to contact the health-service helpline.
Officials are also trying to track down passengers on Swiss Air flight LX318 from Sao Paulo to Heathrow, through Zurich, which landed on February 10. One of the Gloucestershire cases was on the plane.
The flight landed five days before the UK's hotel quarantine scheme was introduced and the government is facing renewed criticism for failing to enforce the system sooner.
"In the case of the sixth case ... we're trying to track down this individual but we have not seen any further community spread," Health Secretary Matt Hancock said on Monday.
"It doesn't change our assessment of the roadmap right now, not least because our goal is to contain this transmission to just these six people."
Vaccines Minister Nadhim Zahawi said the mystery patient did not provide contact details on their coronavirus test form, so Public Health England does not know where they are.
Mr Zahawi said the patient could have undergone a Covid-19 home test as officials at testing centres should check forms are filled out correctly.
He denied that hotel quarantine should have been brought in sooner.
“You can say to me Australia does it much better … but even Australia has had similar challenges on variants,” Mr Zahawi told BBC Radio 4.
He said there was minimal risk to the community where the variants were found, with surge testing under way in five postcode areas near South Gloucestershire.
"Two have been self-isolating," Mr Zahawi told Sky News. "They took a pre-departure test and filled in a passenger locator form.
"So there's minimal reason to believe there will be further spread because they have been isolating correctly.”
British Prime Minister Boris Johnson said during a visit to a school that the government was “going at the right pace” in easing lockdown restrictions.
“Getting all schools open on March 8 is something that we have set our hearts on for a long time and I am confident we will be ready,” Mr Johnson said.
“What we are doing is embarking now on a journey, a one-way road map to freedom, and it is designed cautiously in order to be irreversible.”
Dr Susan Hopkins, strategic response director at Public Health England, said the variant thought to have been first detected in Manaus, Brazil, was similar to the South African strain.
"They have a number of mutations that are suggested to increase transmissibility," Dr Hopkins said.
"Manaus reports that a number of individuals who were infected with this variant were infected twice.
"Prior immunity from infection wasn’t enough to reduce infection and transmission and that could impact on the vaccine."
Prof Graham Medley, from the London School of Hygiene and Tropical Medicine, said the new variants were challenging and could affect plans to resume widespread international travel.
"Our government can make decisions about what happens in the UK but they can’t make decisions about what happens globally," Prof Medley said.
"They can decide the extent to which we have transmission crossing borders.
"It’s a risk that the government has to play off against the risks of new variants arising somewhere else and coming here."
Labour party demands investigation into slow Manaus variant tracking
The developments prompted criticism from the opposition Labour party, which demanded an investigation into why the cases were not identified more quickly.
Yvette Cooper, chairwoman of the home affairs select committee, said news of the variant demonstrated the weaknesses in the UK system.
“It does show, I think, the problems with some of the delays from the government in bringing the stronger measures in, because these cases seemed to arrive around a month after the Brazil variant was first identified, and we were raising with the government the need to bring in the stronger measures and stronger action,” Ms Cooper said.
“It identifies some of the other gaps and weaknesses in the system as well.”
The postal service is trying to help identify the mystery case.
The hotel quarantine scheme came into force on February 15. It means that travellers coming to England from 33 countries, including Brazil, must pay to enter quarantine in a hotel for 10 days.
Before then, arrivals were told to isolate in their homes for 10 days.
Do vaccines work against the Brazilian variant?
Officials are worried that both the Brazilian and South African strains of the virus could undermine Britain's vaccination drive.
The variants have undergone mutations that could make them more contagious.
Scientists are still trying to gather data on how the vaccines work against the new strains, but drugs can be modified if required.
Updated vaccines could be ready within months, meaning a booster shot would be needed to ensure protection among the UK population.
