The UK Health Security Agency said on Friday that the variant AY.4.2 "may have an increased growth rate in the UK compared to" the Delta variant.
But health bosses have urged calm, saying it does not appear this variant "causes more severe disease or renders the vaccines currently deployed any less effective".
Although regular Delta still accounts for most Covid infections in the UK, cases of “Delta Plus” or AY.4.2 have been increasing.
Official data suggests 6 per cent of coronavirus cases are of this type.
Dr Jenny Harries, Chief Executive of the UK Health Security Agency, said: “Viruses mutate often and at random, and it is not unexpected that new variants will continue to arise as the pandemic goes on, particularly while the case rate remains high.”
However, AY.4.2 is not a “variant of concern”, which is the highest category assigned to variants according to their level of risk.
Latest weekly figures for the reproduction number (R) and growth rate of #coronavirus (#COVID19)
Statistics for England as of 22 October:
▶️R value range: 1.0 to 1.2
▶️Growth rate range: +1% to +3%
More info: https://t.co/tQUj8yTEVu pic.twitter.com/DwQoY6sT7i
— UK Health Security Agency (@UKHSA) October 22, 2021
It comes after daily cases in the UK exceeded 50,000 on Thursday for the first time since July.
Prime Minister Boris Johnson has insisted there is "nothing to indicate" that a full lockdown with a "stay at home" order is on the cards this winter.
He said: "I've got to tell you at the moment that we see absolutely nothing to indicate that that's on the cards at all."