An urgent alert was issued tonight to find the missing person thought to be infected with the P.1 variant - first seen in the city of Manaus - after a positive Covid test in England, processed on February 14, came back without a name on it.
The person did not fill in their test registration card and there are fears they could be passing on the mutant strain, which may spread more rapidly and may respond less well to existing vaccines.
Three were Scottish residents who flew from Brazil to Paris and then on to London and Aberdeen.
Passengers who travelled with the infected Brits - days before quarantine hotels were set up - are being told to get tested.
The mystery case is not believed to be linked to the carriers in South Gloucestershire or Scotland because the virus was found to have slight genetic differences.
Officials are now desperately trying to identify and isolate the mystery person, and have appealed to anyone who took a Covid test on February 12 or 13 and has not received a result, or did not complete their test registration card, to call 119 in England or 0300 303 2713 in Scotland as soon as possible.
It is most likely the mystery person took either a home test kit or a ‘test and collect’ service, because drive-in or walk-in test sites have staff on hand to ensure details are filled in.
It is understood health officials do not know at all the location of the test or who took it.
They know which laboratory it was processed at but have not disclosed that information.
The two cases in South Gloucestershire include a person who travelled from Sao Paulo back to London’s Heathrow Airport, and they and their household isolated when they got home.
One of those infected in South Gloucestershire returned to the UK five days before the long-trailed hotel quarantine policy took force for Brits returning from Brazil.
A member of the household developed symptoms, officials said, before getting a test.
There were four cases in that household, two of which were confirmed as the Manaus variant with genetic sequencing.
But officials are awaiting the results of sequencing on the outstanding two tests to see if they were infected by the Manaus strain.
Surge door-to-door testing in South Gloucestershire will begin at 9am on Monday to establish whether there are any other cases of the potentially more transmissible variant in the council area.
Surge testing in five postcodes in Gloucestershire
South Gloucestershire Council said surge testing will take place in the following five postcodes for those who are aged 16 and over and asymptomatic, plus those who travel into those areas for work or to visit someone they are in a support bubble with.
The postcodes fall within the Bradley Stoke, Patchway and Little Stoke areas, and are "different to those that were part of the community surge testing programme which took place between February 7 and 21, the council said.
"There is no connection between the two programmes," it added.
The five postcodes are:
- BS32 0
- BS32 8
- BS32 9
- BS34 5
- BS34 6
As a precaution, officials are re-testing all household contacts of the cases in South Gloucestershire.
Health officials are also following up with people who were on the same flight as the South Gloucestershire patient - Swiss Air LX318 which travelled from Sao Paulo via Zurich to London Heathrow on February 10.
People who were on the Swiss Air flight, and their household contacts, are being asked take a test even at this late stage because they could have residual virus that can be detected.
If you were on that flight and have not yet been contacted, please call 0117 4503174 to arrange a test for both yourself and your entire household.
Public Health England said “up to” six cases had been found and that the sixth suspected case, without a name, currently has no known connection to other two in England.
The person who took the unknown test did not fill in their test registration card, so researchers are only able to see a barcode without the accompanying personal details.
The cases in England were detected on Friday through routine sequencing of the virus.
It is thought Public Health England have sequenced 25 per cent of cases in the most recent full week.
Dr Susan Hopkins, PHE's strategic response director for Covid-19, said: "We have identified these cases thanks to the UK's advanced sequencing capabilities which means we are finding more variants and mutations than many other countries and are therefore able to take action quickly.
"The important thing to remember is that Covid-19, no matter what variant it is, spreads in the same way. That means the measures to stop it spreading do not change."
The World Health Organisation has been informed of the cases, which has been designated "of concern" as it shares key mutations with the variant detected in South Africa.
Three cases in Scotland
Three cases of the Brazil variant of Covid-19 were detected in Scotland.
Following a return to north-east Scotland from Brazil, via Paris and London, three Scottish residents tested positive for the new strain of coronavirus.
All three have been self-isolating since their return to Scotland.
The tests were completed in early February and passed to the UK's advanced sequencing capabilities programme - which detected this new variant.
Due to the potential concerns around this variant, other passengers on the flight used by the three individuals from London to Aberdeen are being contacted.
These three cases are not connected to three cases also identified in England.
Health protection teams, including local clinicians, have assessed each case and their contacts and are arranging protective measures for this small number of potentially exposed individuals.
To provide an extra layer of safety, teams are ensuring people who could have been infected by these first line contacts are also isolated and tested.
This is to ensure all possible precautions are taken as experts learn more about this particular variant.
Clinical and trial data continues to be assessed to examine how the new variant may respond to current Covid-19 vaccines.
Health Secretary Jeane Freeman said: "The identification of this new variant is a concern but we are taking every possible precaution.
"We have identified these cases thanks to our use of advanced sequencing capabilities which means we are finding more variants and mutations than many other countries and are therefore able to take action quickly.
"This new variant demonstrates how serious Covid is and reinforces the need to minimise the spread of the virus.
"We would encourage everyone across the country to adhere to the necessary public health restrictions by staying at home except for essential purposes as this is the single best way of staying safe and stopping the spread of this virus.
"It is now also illegal for anyone to travel to or from Scotland unless it is for an essential reason.
"The Covid vaccination programme is one of three key ways we are working to beat this virus, along with our expanded testing programme to identify cases and break chains of transmission, and the important lockdown restrictions everyone in Scotland must follow.
"These three strands - following expert advice and guidance to suppress the virus, using our expanded testing programme to identify cases and break chains of transmission and rolling out vaccination as fast as supplies allow - are the three critical actions that will see us move, step by step, to protect the public, save lives and a brighter year ahead."
The chairwoman of the Commons Home Affairs Committee, Labour MP Yvette Cooper, said: "This troubling development shows the weaknesses in the Government's Covid border measures.
"The Brazil variant was first identified a month before one of these cases was brought in on February 10 and many weeks after the Prime Minister was warned that indirect flights were a problem, yet the Government delayed putting stronger measures in place.
"We need to know urgently how all these cases have arrived in the country and why they weren't prevented or picked up on arrival so that lessons can be quickly learnt and policies changed to protect the vaccine programme from further cases arriving."
Shadow home secretary Nick Thomas-Symonds said the detection of the variant in the UK was "deeply concerning".
"It is now vital that we do everything we can to contain it," the Labour MP said.
"But this is further proof that the delay in introducing a hotel quarantine was reckless and the continuing refusal to put in place a comprehensive system leaves us exposed to mutations coming from overseas."
Why is there so much concern about the Brazil variant?
P.1 has been deemed a ‘variant of concern’ because it shares important mutations with the South Africa (B.1.351) variant - including E484K and N501Y.
Scientists believe it may respond less well to the vaccine, though there is no data on this yet.
It is also possible it may spread more easily than other variants of coronavirus.
While the South African variant and the separate P2 variant had previously been seen in the UK, these six cases are the first time the P1 variant has been detected in this country.
Professor Stephen Powis, the NHS’s national medical director, has said coronavirus vaccines can be quickly adapted to tackle new strains, following the emergence of the new Manaus variant which may respond less well to existing immunisations.
Professor Powis told BBC News: “The new vaccines which are being used for Covid can be adapted very rapidly so it’s likely that if we do need to change the vaccine that can be done in months, rather than years, which was the case with the more traditional vaccines.”
Brazil and South Africa are among 33 'red list' countries for travel to the UK.
Direct flights from Brazil and South Africa were previously banned to prevent the spread of mutant strains of the disease from being imported.
The quarantine hotel policy to protect the UK against new variants came into force on February 15 after much delay.
Non-UK citizens or residents who have been in or travelled through any of those countries in the previous 10 days will be refused entry to the UK.
British or Irish nationals and those with residence rights in the UK are allowed to enter Britain, however they must quarantine in a Government-approved hotel for 10 days at a cost of £1,750 per person.
-+They will be allowed to leave their quarantine hotel after 10 days as long as they test negative for Covid.
Those who have returned to the UK after being in Brazil or South Africa have done so by flying to Britain via another country.
Earlier, Chancellor Rishi Sunak told the BBC's Andrew Marr Show there is no evidence of newly discovered coronavirus variants spreading after concerns that case rates are rising in one in five areas of England.
He added: "That's not what I've seen in any of the data."
Pressed if there was any evidence of more new variants, he said: "No."