The Prime Minister is expected to agree to put the final easing of controls on hold for up to four weeks when he meets senior ministers and officials on his return on Sunday from the G7 summit in Cornwall.
It could mean that lockdown lifting – which had been slated for June 21 under the Government’s road map – will be put back to July 19.
The move, expected to be confirmed in a formal announcement on Monday, will be a bitter blow for many businesses, particularly in the hospitality sector, which had been pinning their hopes on a full summer reopening.
Mr Johnson is also likely to face opposition from some of his own MPs who have been chafing for months over the restrictions and will be furious at any further delay.
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However, a poll by Opinium found significant public support for a postponement, with 54% in favour and 37% against.
Scientists have been pressing for additional time to get more people vaccinated – particularly those in younger age groups – before controls are relaxed.
Studies have shown that people who have received only one dose of the vaccine have significantly less protection against the Delta variant – first identified in India – than those who have had two jabs.
Public health officials believe a delay would also give more opportunity to control the spread using surge-testing techniques which proved successful in Bolton, which was the first Delta variant hotspot.
Speaking in Cornwall on Saturday, a downbeat Mr Johnson acknowledged that the rise of the variant was a matter of “serious, serious concern”.
With infections and hospital admissions both rising, he said that it was not yet clear to what extent that would feed through into more deaths.
However, in order to ensure the final lockdown lifting was “irreversible”, he said that it may be necessary to give the vaccines “extra legs” in the race against the virus.
Some ministers however were reported to be even more pessimistic, with one telling The Sunday Telegraph that they had a “very short window” in which to open up, otherwise controls could have to stay in place until spring of next year.
“I am very worried the people who want to keep us shut down now want us to keep us shut down permanently and are aiming for ‘zero Covid’,” the unnamed minister was quoted as saying.
“Once you start delaying to the spring you’re making this type of control of people’s lives semi-permanent.”
Scientists now estimate that 96% of all new cases of coronavirus are attributed to the Delta variant.
The latest figures from Public Health England (PHE) show there have been 42,323 cases of the Delta variant confirmed in the UK, up by 29,892 from the previous week.
It estimates the strain is 60% more transmissible compared with the previously dominant Alpha, or Kent, variant, and that cases are doubling every four-and-a-half days in some parts of England.
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