Prime Minister Boris Johnson faces a "very difficult" call on whether to drop restrictions on June 21 given the "more negative direction" of the data, according to a leading expert.
Professor Neil Ferguson, whose modelling was instrumental to the UK locking down in March 2020, said a "cautious" approach is needed as the Government balances the potential risks against a desire for normality.
The full effect of easing some restrictions on May 17, such as indoor mixing in pubs, is yet to be understood and further data is required, Prof Ferguson added.
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For the Government, Communities Secretary Robert Jenrick said there is "nothing at the moment that suggests that we won't be able to move forward" with the next stage of lifting restrictions on June 21.
Mr Johnson has come under pressure to move ahead with the June 21 unlocking - dubbed "freedom day" by some - given the huge uptake of Covid-19 vaccines in recent months.
But questions remain over the impact of the so-called Indian variant of Covid, also known as the Delta variant, on hospital admissions and deaths.
Mr Jenrick, appearing on BBC Radio 4's Today programme, said: "We've got a further 10 days until we are going to make that decision on or around June 14, so during that period we'll see where are we with hospitalisations, with deaths, where are we with the vaccine rollout - we're doing everything we possibly can to expedite that - and then at that point, we'll make our final decision."
Asked whether measures such as wearing masks and working from home could continue after June 21, Mr Jenrick replied: "Well, there are options that are clearly available to the Government."
He added: "We set out within the road map what would be expected to happen at the next stage and we want to try to stick to that if we possibly can.
"All of us are moving everything we can to achieve that. But, of course, we keep these things under review and we're also asking people to continue to exercise caution in their daily lives."
