Boris Johnson has said the government must “be cautious” as it decides whether to end all Covid restrictions in England on June 21.
Cases are rising as the Delta variant spreads, with details of the next step on the “roadmap” due on Monday.
The prime minister told the BBC it was important any easing of restrictions was “irreversible” and warned that hospital admissions were increasing.
The BBC has been told a delay of up to four weeks is being considered.
Senior medical advisers urged a brake to the final easing of lockdown restrictions, which, if it went ahead in full, would mean removing limits on social contact and the number of people allowed into homes.
Pubs, clubs, theatres and cinemas would also be allowed to operate without capacity limits, with sports events taking place in full stadiums, nightclubs reopening and limits of the number of wedding guests going.
Asked by BBC political editor Laura Kuenssberg whether all restrictions would now be lifted, Johnson said people would have to wait until Monday to find out.
“What I can certainly say is we are looking at the data, continuing to do that, but what you can certainly take is… the roadmap was always cautious but irreversible, and in order to have an irreversible roadmap, we’ve got to be cautious.”
A further 7 738 lab-confirmed cases of the virus were reported in the UK on Saturday, and a further 12 people recorded to have died within 28 days of a positive test.
Infections continue to rise, with 50 per cent more cases reported in the past seven days than the previous seven.
Answering questions at the G7 summit in Cornwall earlier, chief scientific adviser Sir Patrick Vallance would not be drawn on the decision about 21 June, but said the “Delta variant [is] increasing in the UK”.
He said there were lessons from the pandemic that could continue to apply in everyday life – such as self-isolating after symptoms of any infectious disease, the importance of ventilation, and hand hygiene.
The Delta variant, first identified in India, now accounts for nine in 10 UK coronavirus cases.
It is roughly 60 per cent more transmissible than the Alpha – or Kent – variant, Public Health England data suggests.
The government put India on the “red list” of places to which travel is banned on 23 April, two weeks later than Pakistan and Bangladesh, which had fewer cases per million at the time.
The prime minister defending the timing of the decision, saying: “Pakistan had about 13 times as many variants of concern or variants of interest as as India at that stage.”
“Yet we put India on the red list on 23 April, which was days before it was even identified as a variant under investigation.”
Johnson, who is currently hosting the G7 summit in Carbis Bay, Cornwall, said the government had made “a massive progress with the vaccination programme”.
“It’s done a huge amount of good – but you have got to be cautious to be irreversible,” he added.
“Again you have hospitalisations up, you’ve got cases up. There are grounds for caution.”
On Friday, the British Medical Association joined public health officials in calling for a delay to ending restrictions. (BBC)
