Plans to ease social distancing are in "disarray" as Brits could be left waiting as late as mid-June to find out rules for the summer.
Boris Johnson had pledged to update England by the end of May on whether social distancing rules could end from June 21.
But with the Indian variant spreading to at least 86 council areas, Downing Street have admitted that date might be pushed back.
While crucial data is expected to roll in over the coming days and weeks, it could take time before the full picture is known.
Hailing new data at Prime Minister's Questions, Boris Johnson today announced "we have increasing confidence that vaccines are effective against all variants, including the Indian variant."
But he made no comment on how transmissible the new variant is - the key issue that will decide if lockdown can ease on time.
And No10 later admitted he was simply talking about public data, with no knowledge yet about the variant's transmissibility.
Experts have warned it could scupper lockdown easing if it is, say, 50% more transmissible than the UK Kent variant.
Asked where Boris Johnson got his figures from, a No10 spokesman said: "There’s a number of data sets we’re looking at, that includes things like hospitality rates [sic], case rates, and a number of studies published around the world which continue to show high levels of efficacy against variants."
According to the Telegraph, it could be as late as June 14 before Brits know for sure what distancing rules will apply after June 21.
Sources played down that report, telling the Mirror the decision on social distancing rules - first pledged by the end of May - was not expected to be that late. But they did warn it would take more time.
Another government source told the Mirror: "Over the coming days and the next week or two we’ll be getting a lot of data coming in - including hospitalisations in the areas where the Indian variant is seeing a rise in cases.
“We’re learning more day by day. It really is a case of seeing what the data says. This is the roadmap working as it should.”
SAGE member Prof Neil Ferguson today revealed there is a "glimmer of hope" in new data that may suggest the B.1.617.2 variant's advantage has "dropped a little bit".
But Prof Ferguson also said it could be "two to three weeks" before scientists have enough data to know if the June 21 lockdown easing will be knocked off course.
The government had always said it would only say by June 14 whether step four of the roadmap - which includes dropping social distancing rules, reopening nightclubs and allowing big gatherings indoors - could go ahead on June 21.
However, Boris Johnson had claimed there would be updates by around May 24 on whether full-sized weddings could go ahead - giving 28 days for banns - and by May 31 on future social distancing rules.
One government source told the Telegraph: "The general mood is a bit more cautious." Another said: "It's been thrown into disarray by the Indian variant."
The lack of information will leave stricken hospitality firms and big festivals in limbo.
Prof Ferguson said if the variant was widespread and highly transmissible, then locking down hotspot areas "may work in those areas, but just allows the rest of the country to reach a high infection level - and we know what the consequences of that were last year.
"We're in a different situation now we have high levels of vaccine coverage, so the real challenge for us as scientists and for the Government is to try and calculate - is that wall provided by vaccinations sufficient for us to keep the consequences of this Indian variant at a manageable level?"
According to reports, there are three options for what happens on June 21, when it had been hoped all legal restrictions would end.
Either it will go ahead as planned, or there will be local restrictions in some areas, or some June 21 easings will be delayed for the whole country.
Regions could be thrown into a ‘Tier 4’ system with pubs, restaurants and non-essential shops closed and a stay-at-home order, The Times reports.
Businesses in areas slapped with restrictions would be able to claim grants of up to £18,000 through their local council.
It comes as Matt Hancock is expected to give a Downing Street press conference at 5pm today.
The Health Secretary is set to give a general update on Covid-19 as fears mount about the Indian variant.
Two days ago he told MPs there were more than 2,300 cases of the more transmissible strain detected in the UK.
Boris Johnson is facing questions about whether he was too late to add India to the red list when cases were soaring in early April.
Ministers have insisted the variant was only deemed of concern well after India was put on the red list.
But B.1.617.1 - which is closely related to the B.1.617.2 strain worrying experts - was deemed under investigation on April 1.
That was days before Pakistan and Bangladesh - but not India - were put on the red list, despite Covid positivity rates being higher in passengers from India than from Pakistan.
