Further doubt was cast on the full reopening planned for 21 June after a further 6,238 lab-confirmed cases of coronavirus were recorded in the UK - the highest daily figure since 25 March.
One scientist helping advise the government warned that if numbers in hospital rise because of the Indian variant, the 21 June unlocking may not go ahead.
Separately, Professor Neil Ferguson said the coronavirus data were “pointing in a negative direction” as the Indian - or Delta - variant had doubled across the UK every nine days.
He said the variant, first identified in India, was likely to be 60 per cent more transmissible than the previously dominant Alpha variant that originated in Kent.
Surge testing has begun in Bradford and two areas of Kent after cases of the variant were detected there.
Health secretary Matt Hancock said the Government “always expected cases to rise” as lockdown was eased.
The increase in the spread of the coronavirus is reflected in how reproduction number, or R value, in England has risen. It is now between 1 and 1.2, according to the latest government figures. Last week, it was between 1 and 1.1.
