Four people who contracted the Indian variant of coronavirus have died, official data shows.
It comes after cases of the mutant strain more than doubled in a week in the UK, with concerns growing that the new variant could scupper lockdown easing.
According to data published by the government, the four deaths from the B.1.617.2 strain of the virus took place between 5 May and 12 May.
Scientists do not believe vaccines are less effective on the Indian mutation but they do think it could be more transmissible than the Kent variant.
The Indian mutation has only recently been detected in the UK and is being closely monitored, with more than 1,300 cases recorded as of May 12.
Surge testing is under way in areas of the North West of England where cases involving the variant of Covid are on the increase.
Infections appear to be at their highest in Erewash in Derbyshire and are particularly prevalent in the north west of England, in areas including Bolton, Greater Manchester, and Sefton in Merseyside.
More vaccine doses have been sent to Bolton, while 800,000 PCR tests have been sent to 15 separate areas of the England, including parts of London and Merseyside.
However, broader risk levels remain lower than they were for much of the winter due to low levels of Covid infections overall.
Early research suggests the Indian variant is not resistant to existing vaccines but there are fears it is at least as transmissible as the Kent strain.
Speaking on Thursday, Boris Johnson said the government is “anxious” about the Indian variant and is “ruling nothing out”.
The Prime Minister will host a coronavirus press conference from Downing Street at 5pm on Friday.
A spokesperson said he will be joined by England’s chief medical officer Professor Chris Whitty.
Vaccines minister Nadhim Zahawi said the public must help suppress the Covid infection rate in the face of the Indian variant if plans to lift restrictions are to stay on track.
He urged people in the 15 areas of England with spread of the Indian variant of concern to follow local health advice, get tested and isolate if they test positive.
Meanwhile he warned the wider public to “do their bit” to help fight the spread by taking two Covid tests a week.
He added: “We have got to break the cycle of infection, because one of those big tests was infection rates have to be suppressed, and the other big test is variants.
“If those cause a problem, then the tests will fail. The four tests have to be met for June 21.”
One option also being considered by clinical advisers to the government is to bring forward the date for second doses of vaccine for the elderly and vulnerable in regions where the Indian variant is spreading.