The Manaus variant of coronavirus, discovered in both England and Scotland, has also been reported in 15 countries not on the UK's so-called 'red list'.
Red list countries are those which require any incoming visitors - who must be UK nationals - to quarantine in a designated hotel for 10 days on arrival, and include Brazil, Peru and Portugal.
Mandatory quarantine is in place to prevent new variants of coronavirus entering the UK, but - according to a list compiled by the World Health Organisation (WHO) - the most recent variant of concern (the Manaus variant) is present in 15 countries not included on the red list.
Scientists and health experts fear the Manaus (P1) variant - so called because it emerged out of the Brazilian city of Manaus - may be more transmissible than previous variants, and may be able to evade vaccines currently available.
Yet while Brazil is on the UK's red list for travel, WHO says the P1 variant has now been discovered in 15 countries which are not on the list, including France, Germany, Japan, Spain, Canada, the US, Mexico, Italy, India and the Republic of Korea.
Further reports - which are yet to be verified - suggest the variant may also be present in some other countries including Ireland, Sweden, China, Turkey and Ireland.
The red list 'could go out of date at any time'
Health Secretary Matt Hancock has assured the public that the number of causes caused by the P1 variant in the 15 non-red list countries was "exceptionally low".
Some experts, however, are worried the red list does not provide enough protection against emerging variants of the virus.
Dr Julian Tang, a virologist and University of Leicester honorary associate professor, told the Guardian the Government’s red list “could go out of date at any time” because of the time it takes to identify and sequence coronavirus cases.
“We saw that Ireland reported three cases of the P1 Brazilian variant about 10 days ago,” he continued.
“It was not surprising to see other imported cases in the UK mainland soon afterwards - and these cases may have already created others here."