(AFP) - The British government on Monday lifted pandemic restrictions on daily life in England, scrapping all social distancing rules in a step slammed by scientists and opposition parties as a dangerous leap into the unknown.

From midnight (2300 GMT Sunday), nighclubs reopened and other indoor venues were allowed to run at full capacity, while legal mandates covering the wearing of masks and working from home were scrapped.

Prime Minister Boris Johnson -- who is self-isolating after his health minister was infected -- urged the public to remain prudent and for any laggards to join the two-thirds of UK adults who are now fully vaccinated.

He defended the reopening -- dubbed "freedom day" by some media -- despite scientists' grave misgivings after daily infection rates in Britain topped 50,000, behind only Indonesia and Brazil.

"If we don't do it now, then we'll be opening up in the autumn, the winter months, when the virus has the advantage of the cold weather," the prime minister said in a video message.

This week's start of summer school holidays offered a "precious firebreak", he said.

"If we don't do it now, we've got to ask ourselves, when will we ever do it? So this is the right moment, but we've got to do it cautiously."

In a bid to demonstrate a bit of caution, vaccines Minister Nadhim Zahawi told the BBC he would continue to wear a mask in "crowded indoor places".

But Jonathan Ashworth, the opposition Labour party's health spokesman, said the government was being "reckless", echoing experts who say the reopening endangers global health.

"We are against opening up without any precautions in place," Ashworth told BBC television, attacking in particular the government's plan on masks.

- 'A new chapter' -

After the success of the vaccination programme -- which has now offered at least one dose to every adult in Britain -- the government says any risks to hospital care are manageable.

But professor Neil Ferguson from Imperial College London warned that Britain was on course for 100,000 cases a day, as the Delta variant runs out of control.

"The real question is, do we get to double that or even higher?" he told BBC television.

"We could get to 2,000 hospitalisations a day, 200,000 cases a day, but it's much less certain," he said.

Despite the risks, in Leeds in northern England, there was a queue outside Fibre, a night club reopening on Sunday evening, and the dance floor was packed with no masks in sight.

"I thought, well, we missed New Year's, so why not come out and celebrate?" said Nicola Webster Calliste, 29.

"It's like a new chapter."

- Warning light -

But medics warned that relaxations could push up case numbers enough to put severe pressure on the National Health Service (NHS) and risk seeding new variants, even though Britain is suffering far fewer deaths than in previous waves.

Senior Conservative MP Jeremy Hunt, a former health secretary, said the government should learn from Israel and the Netherlands, which have been forced to reverse recent relaxations.

"The warning light on the NHS dashboard is not flashing amber, it is flashing red," he told BBC radio.

Scotland and Wales, whose devolved governments set their own health policy, said they would maintain the mandate on face coverings among other restrictions, despite England's moves to lift measures.

Fully vaccinated residents returning from so-called "amber list" destinations in Europe no longer have to quarantine -- although in a last-minute policy shift, the government has kept the requirement in place for France.

Also staying in place are requirements to self-isolate after a close contact, which have forced millions off work or school in recent weeks, leading to industry warnings of severe economic disruption.

After their contact with Health Secretary Sajid Javid, Downing Street initially said Johnson and finance minister Rishi Sunak would get tested every day instead of self-isolating.

But after a public and political outcry, Downing Street staged a hurried U-turn.

Johnson, who was in hospital with Covid last year, will remain at the prime minister's country retreat at Chequers northwest of London until July 26.

Others urged the government to stick to the cautious global consensus on tackling the pandemic, rather than acceding to the libertarian instincts of Johnson and other Conservatives.

The government's stated approach of lifting controls now before any winter surge of respiratory disease is marked by "moral emptiness and epidemiological stupidity", said University of Bristol public health expert Gabriel Scally.

© Agence France-Presse