Three cases were found in England and another three in Scotland.
Two of three cases found in England were from a household in the South Gloucestershire area that had a history of travel to Brazil. A third, currently unlinked, case has yet to be identified, Public Health England said on Sunday.
The risk to the wider community from the Gloucestershire cases was considered low but as a precaution officials were moving quickly to deploy testing and increasing the sequencing of positive coronavirus samples from the area, PHE said.
The Scottish cases were not linked to the ones in England.
The P.1 variant detected in Manaus shares some mutations with a variant first identified in South Africa and it is possible that it might respond less well to current vaccines, PHE said.
Susan Hopkins, PHE's strategic response director for Covid-19, said Britain's advanced gene sequencing capabilities meant it was finding more variants and mutations than many other countries.
Late last year Britain detected a more transmissible variant of coronavirus that is believed to have originated near London and that led to a sharp rise in cases in the country and beyond.
"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," Hopkins said.
PHE and test and trace officials system were following up with all passengers on Swiss Air flight LX318 from Sao Paulo to London via Zurich, which landed at London Heathrow on Feb. 10, to test them and their households.
All three of the Scottish cases were identified in people who returned to the country via Paris and London who self-isolated for the required period of 10 days.
"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," the Scottish government said.
20 MILLION GET JABS
More than 20 million people across the United Kingdom have now received their first Covid-19 vaccine shot, data showed on Sunday as the country made more progress with Europe's fastest vaccination programme.
Prime Minister Boris Johnson said the milestone represented "a huge national achievement and he paid testament to the country's health, workers, volunteers and armed forces.
"I urge everyone to get the jab when called," Johnson said. "Every jab makes a difference in our battle against Covid."
Britain has suffered the highest Covid-19 death toll in Europe - it currently stands at 122,849 - and the heaviest economic shock among big rich countries, according to the headline measures of official data.
But the pace of its vaccination roll-out has raised the prospect of a gradual lifting of its current lockdown restrictions between now and the end of June.
On Sunday, finance minister Rishi Sunak promised to help the economy while the country remains under restrictions.
In a budget statement on Wednesday, he is expected to announce more borrowing on top of his almost 300 billion pounds ($418 billion) of COVID-19 spending and tax cuts.
Official data showed a total of 20.09 million people in Britain have received their first dose of a Covid-19 vaccine and almost 800,000 have received a second dose.
Last week, Britain said more than one in three adults had received their first vaccination.
Britain also reported on Sunday a further 6035 cases within the previous 24 hours, and 144 more deaths within 28 days of a positive test.
The latest figures meant cases over the past seven days were down 21.2% compared with the previous seven-day period of February 15-21, and deaths were down 33.5%.
