The number of coronavirus cases has soared by another 7,490 just hours before Boris Johnson reveals his decision on the June 21 unlocking.
It represents the highest rise in cases on a Sunday since February 21, when 9,834 new infections were recorded.
The Prime Minister is widely expected to be preparing to delay 'freedom day' by several weeks or even a month, according to reports in recent days.
Officials are worried that the spread of the Indian variant could speed up if restrictions are eased further.
Eight more deaths were reported today. Last Sunday, a total 5,341 new cases and six more fatalities were reported.
In recent days the numbers have been topping 7,000 new positive cases nationwide daily.
On Saturday, another 7,738 new cases and 12 deaths were reported.
Scientists have been urging the Government to give the vaccination rollout more time to curb the spread of the virus before any more measures are relaxed.
The fourth phase of Mr Johnson's roadmap out of lockdown is in doubt as the 'Delta' variant, which scientists say is even more virulent then the Kent strain, continues to push up case numbers.
The strain is not believed to be more deadly than its predecessors, and a steady rise in daily cases and hospital admissions has not been accompanied by a sharp increase in deaths, reports The Mirror.
Health officials have credited the vaccine rollout with keeping severe cases of the virus at bay, as more than three-quarters of the UK's adult population has now had at least one dose.
Sunday's figures show more than 41.5million people have received at least one dose of the vaccine, and nearly 30m have received two.
The PM has vowed every adult in the UK will be offered a jab by the end of July.
Speaking from the G7 summit in Cornwall this week, Mr Johnson told Sky News he is less than optimistic about the June 21 unlocking goal.
He said he was prepared to be "cautious" over the fourth and final stage in his roadmap out of lockdown.
The next phase in the easing of restrictions would see sectors closed throughout the pandemic finally allowed to reopen.
So-called 'freedom day' would bring the return of nightclubs, and large mass gatherings for cultural and sporting events.
The PM told the broadcaster it was "clear" the Delta variant was "more transmissible" and driving the increase in the number of people in hospital in the UK.
"Now we don't know to what extent that exactly is going to feed through into extra mortality but, clearly it's a matter of serious, serious concern," he said.
The PM admitted he was less optimistic now than he was at the end of May.
He hinted he could delay the next phase of easing Covid measures on Monday, telling Sky: "What we want to do is make sure that the roadmap is irreversible - but you can't have an irreversible roadmap unless you're prepared to be cautious."
