Rising numbers of coronavirus cases and the emergence of the new, more transmissible variant first identified in India have put the final stage of England’s lockdown easing in jeopardy.
Health Secretary Matt Hancock said the Government was "absolutely open" to delaying the final step in Boris Johnson’s reopening roadmap, which was the strongest indication yet that the so-called "freedom day" might be delayed.
However, Downing Street said that data emerging over the coming week will be "crucial" in deciding whether all legal coronavirus restrictions can end as hoped.
The Prime Minister’s official spokesman said: "There still remains nothing in the data currently to suggest Step 4 can’t go ahead at the earliest date. But we do need to look very closely at the data over this coming week."
The Government has committed to announcing the plans for the June 21 reopening next Monday, on June 14.
This week, ministers will receive the most up-to-date coronavirus data as well as papers setting out the options from scientific advisers and officials before making a decision.
Here we look at what might happen if Step 4 of the roadmap is delayed.
What is due to happen on June 21?
According to the Government’s roadmap, Step 4 would see all legal limits on social contact removed.
It is hoped that the last indoor venues which remain closed, including nightclubs, will reopen and restrictions on large events and performances will cease to apply.
June 21 poll
Why might lockdown easing be delayed?
Mr Hancock said the emergence of the Indian (also known as Delta) variant, which is believed to be up to 40 per cent more transmissible than the Kent strain, had made the "calculation" on whether to proceed with unlocking "more difficult".
Scientists suggested that a steadily rising number of hospitalisations should delay the final stage of the roadmap.
Downing Street said the data emerging over the coming week would be "crucial" in deciding whether the remaining restrictions could end. The Prime Minister’s official spokesman said the new data will help show "whether or not the excellent vaccine rollout programme has sufficiently severed that link between the increase in cases … and that subsequently leading to hospitalisations and deaths".
What could happen instead?
Mr Johnson is reportedly considering delaying the end of restrictions by at least two weeks in order to allow more people to be fully vaccinated.
Mr Hancock also implied that some measures may remain in place after June 21. This could include further working from home, social distancing in bars and restaurants and mask wearing.
If the Government decides not to proceed with Step 4 of the roadmap, some indoor venues such as nightclubs would also not be allowed to reopen as planned.
Limits on audiences in theatres, cinemas and sports events may also remain in place.
What are the scientists saying?
A Sage member said this week would be "absolutely critical" in determining whether the June 21 unlocking would go ahead as planned, but added that "we certainly don’t want to go on delaying forever".
Professor Dame Anne Johnson said more data was needed to make a decision. She told Sky News that there had been a "significant uptick" in the number of cases in the past week or two, meaning that reopening as planned would be a "very finely judged decision".
However, NHS leaders have said that scientific modelling has been crude and unreliable at predicting the pandemic, and they warned against using it to decide whether to release restrictions on June 21.
Chris Hopson, the chief executive of NHS Providers, said trusts were "sceptical" about the fitness of models to provide useful forecasts for the pandemic.
How does this affect businesses?
UK business chiefs have warned MPs that a "generation" of firms could face collapse without further support, after piling up billions of pounds in debt during the pandemic.
Hospitality bosses have said that delaying freedom day would push many struggling businesses "closer to the cliff edge".
Kate Nicholls, chief executive of UK Hospitality, said: "The ongoing uncertainty around the roadmap is causing significant distress to hospitality businesses and operators.
"It is crucial that the Government commits to dropping the restrictions on June 21. Any delay in the roadmap would have a devastating effect on an already fragile sector."
Government support for affected businesses remains in place until September.
What is currently allowed?
Most of the legal restrictions on meeting outdoors were dropped on May 17 after the Government pushed ahead with Step 3 of Mr Johnson’s roadmap.
People are allowed to meet indoors too, but the rule of six or two households still applies.
Indoor dining in restaurants is already permitted and customers are no longer required to purchase substantial meals with alcoholic drinks, nor to stick to a curfew.
Gyms have reopened and certain larger performances and sporting events in indoor venues have resumed.
Up to 30 people are able to attend weddings, receptions and wakes, as well as funerals.
What is permitted in the other UK nations?
As of Monday in Wales, groups of up to 30 people can meet outdoors, including in private gardens, while up to three households can meet indoors.
The Welsh government is yet to give a date for the reopening of larger venues providing live performances or for events such as outdoor music festivals.
Plans to ease lockdown restrictions in much of Scotland have been paused, but restrictions were reduced in Glasgow, which had been kept in Level 3 restrictions due to a spike in cases.
Restaurants, cafes, bars and other hospitality venues in Northern Ireland can operate indoors, with six people allowed to sit together from unlimited households with table service only.