Scientists have identified 16 cases of a new coronavirus variant in the UK, health officials have announced.
All those who tested positive and their contacts have been traced and advised to isolate, Public Health England said.
Variants of Covid-19 may be identified as either under investigation or of concern.
The new variant, which is understood to have originated in the UK, was designated as under investigation on 24 February.
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New variants emerge regularly, and experts are conducting frequent analysis to see which are of concern and which are not.
Cases of the new variant, referred to as VUI-202102/04, were first identified on 15 February.
It contains a mutation called E484K, which is found in two other variants under investigation already present in the UK, but it does not feature a mutation called N501Y that is present in all variants of concern, health chiefs said.
Scientists are now tracking four variants under investigation and four variants of concern in the UK, including those detected in South Africa, Brazil, Kent and Bristol.
Additional testing is being made available for targeted areas of England to suppress the spread of variants of concern.
It includes surge testing in South Gloucestershire after cases of the Manaus variant were discovered there.
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This variant of concern, known as P1, was detected in Brazil and in travellers from Brazil to Japan.
P1 is thought to be more transmissible than earlier forms of the coronavirus, and has driven a second wave of infections in Brazil.
Six cases have been found in the UK: three in Scotland and three in England.
On Tuesday, the hunt for a missing person infected with the Manaus variant had been narrowed down to 379 households in southeast England.
Elsewhere, additional testing in targeted parts of London and Stockton-on-Tees, in County Durham, aims to suppress the spread of the South African variant of concern.
A total of 59 cases of the South African variant have been found in England where no travel links could be established.
And 26 cases of a P2 Brazil variant, which is of less concern, have been found in England where no travel links could be established, Public Health England said.