Cases of the Indian coronavirus variant have doubled in the space of a week, new data shows.
As of Wednesday, Public Health England said there had been 6,959 confirmed cases of the B.1.617.2 variant of concern – up 3,535 from 3,424 a week ago.
Health secretary Matt Hancock said at Thursday's Downing Street press conference that up to 75% of all COVID-19 cases in the UK could now involve the variant.
The continued spread of the variant is raising fresh doubts over the government's plans to lift all lockdown restrictions in England on 21 June.
At the same briefing, Dr Jenny Harries, chief executive of the UK Health Security Agency, said the "pure data... looks quite worrying".
However, she explained the rise in cases could also be linked to the increase in testing in "hotspot" areas.
Dr Harries explained: "I think it is really, really just on the cusp at the moment.
"If we see cases rise, we’re not clear yet quite whether that is a rise in variant cases taking off, or whether it’s actually a rise because we are actively – quite rightly – detecting them and challenging these chains of transmission."
Hancock had earlier told MPs "it’s too early now to say" whether lockdown will end as planned in three-and-a-half weeks' time.
Watch: Matt Hancock casts serious doubt on 21 June lockdown easing
His cautious outlook was later contradicted by Boris Johnson, who told reporters: "I don’t see anything currently in the data to suggest that we have to deviate from the road map."
However, the prime minister then contradicted himself as he added: “But we may need to wait."
Two leading scientists, Prof Neil Ferguson and Prof John Edmunds, have also questioned whether the 21 June unlocking should go ahead.
Prof Ferguson, the scientist whose modelling convinced the government to impose the first lockdown, told BBC Radio 4’s Today programme on Thursday that the 21 June date "is rather in the balance" as the UK "can’t cope with [an infection surge] being too large".
Scientific Advisory Group for Emergencies (Sage) member Prof John Edmunds, speaking on ITV's Peston show on Wednesday night, was also asked if Johnson should unlock on 21 June.
"No," he said. "At the moment, anyway, it looks a little bit risky of course. The Indian variant is taking off in a number of places."
He added: "Encouraging people to go back to normality would be very rash at the moment, so I hope that doesn't happen for a little while at least."
However, Tim Spector, lead scientist on the Zoe COVID Study app and professor of genetic epidemiology at King’s College London, said data "indicate vaccines are still effective against the Indian variant".
He cited relatively low case numbers as well as hospital admissions and deaths.
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