There are signs the UK is in the early stages of a third wave of coronavirus infections, a scientist advising the UK government has said.
Professor Ravi Gupta, from the University of Cambridge, said although new cases were "relatively low" the Indian variant had caused "exponential growth", reports the BBC.
He said ending Covid restrictions in England on 21 June should be postponed.
UK's Environment Secretary George Eustice said the government could not rule out a delay to the planned lockdown easing.
On Sunday, the UK reported more than 3,000 new Covid infections for a fifth successive day.
Prior to this, the UK had not surpassed that number since 12 April.
When asked whether the UK was already in a third wave of infections, Gupta said: "Yes, there has been exponential growth in the number of the new cases and at least three-quarters of them are the new (Indian) variant."
"Of course the numbers of cases are relatively low at the moment - all waves start with low numbers of cases that grumble in the background and then become explosive, so the key here is that what we are seeing here is the signs of an early wave," he added.
However, he said the number of people who have been vaccinated in the UK meant this wave would probably take longer to emerge than previous ones.
"There may be a false sense of security for some time, and that's our concern."