Boris Johnson has announced that the final stage of England's reopening will be delayed by four weeks amid fears that the NHS could be overwhelmed by a new wave of Covid cases caused by the delta variant.
During a No 10 press briefing, the Prime Minister announced that the restrictions, which had been due to end on June 21, will now remain in place until July 19.
A check two-weeks into the four-week delay will be conducted to see whether the situation has improved, but Downing Street officials said it was "unlikely" the plan would change.
Johnson said that the government had made the decision after cases of the delta variant increased by 64 per cent across England in a week.
He added that the link between infection and hospitalisation had been "substantially weakened" but "not completely stopped", citing a 50 per cent increase in hospitalisations in the last week.
"Now is the time to ease off the accelerator," he said.
"By being cautious, we now have the chance over the next four weeks to save many thousands of lives."
The delay to the end of restrictions will mean social distancing rules, wearing face masks, sitting in groups of no more than six inside and 30 outside, and keeping nightclubs shut will remain in force.
However, weddings will be able to go ahead and are no longer restricted to a 30-guest limit.
The Prime Minister also brought forward the government's target of offering a first jab to every adult to July 19, to coincide with the new reopening date. Adults aged 23 and over will be able to book vaccine appointments from tomorrow.
Julian Bird, chief executive of the Society of London Theatre and UK Theatre, said: "The proposed four-week delay to full reopening of live entertainment venues will have serious implications for many theatres and performing companies around the country.
"This delay not only impacts productions and theatres preparing to open in the next few weeks, but also shows currently running socially distanced, which had planned to increase their capacity - and producers making the difficult decision whether to start rehearsals for shows due to open in late July or August, with thousands of jobs hanging in the balance.
"Particularly at risk are large-scale commercial productions, which have received little or no Cultural Recovery Fund support and cannot survive under social distancing.
"We urge the government to consider greater support for affected theatre organisations, by offering a tailored insurance scheme, allocating the remainder of the Cultural Recovery Fund, and extending full furlough and the business rates holiday."
Mayor of London Sadiq Khan said: "Many of our businesses are already struggling for survival, and the announcement today will add to their worry and anxiety.
"The planned reduction in financial support at the end of June could now have dire consequences for jobs and livelihoods, pushing more businesses in sectors such as culture, nightlife and hospitality to the brink of collapse.
"The government must now act urgently to extend economic support to all businesses who need it - including extending the full business rates holiday, the evictions moratorium and the existing furlough scheme until all restrictions are lifted."