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'Freedom Day': England reopens despite skyrocketing Covid cases, Boris Johnson isolating

"I don't think we should underestimate the fact that we could get into trouble again surprisingly fast," the U.K.'s chief medical officer warned.

Almost all lockdown restrictions were lifted in England on Monday despite a rise in Covid-19 cases, warnings of supermarket shortages and Prime Minister Boris Johnson's forced self-isolation.

Although the U.K.'s chief medical officer, Chris Whitty, has warned of potential "trouble," masks will no longer be required as of Monday, dubbed "Freedom Day" by certain sections of the media.

Nightclubs and sporting events will also be free to function at full capacity in England, and the government will no longer advise people to work from home.

In other parts of the U.K. — Scotland, Wales and Northern Ireland — devolved governments are taking more cautious steps and will not reopen fully.

Johnson performed a rapid political U-turn on Sunday and his Downing St. office said he would spend 10 days self-isolating after he came into contact with a confirmed coronavirus patient — reversing an earlier announcement that he would not have to quarantine which was met with widespread dismay.

Johnson and Treasury chief Rishi Sunak were alerted overnight by England's test-and-trace phone app. Johnson had a meeting Friday with Health Secretary Sajid Javid, who tested positive for Covid-19 on Saturday. Javid, who has been fully vaccinated, said he was experiencing mild symptoms.

Johnson's office initially said he and Sunak would take daily coronavirus tests as part of an alternative system being piloted in some workplaces, including government offices.

Less than three hours later, after an outcry over apparent special treatment for politicians, Downing Street said Johnson would self-isolate at Chequers, the prime minister's country residence. It said Sunak also would self-isolate.

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Johnson's big day was also marred by "pingdemic chaos" as a National Health Service app ordered hundreds of thousands of people to self-isolate — prompting warnings supermarket shelves could soon be emptied as businesses across England faced a shortage of workers.

"If we don’t do it now we’ve got to ask ourselves, when will we ever do it?" Johnson said in a video posted to social media.

"This is the right moment but we’ve got to do it cautiously. We’ve got to remember that this virus is sadly still out there."

Britain recorded 54,674 new Covid-19 cases Saturday — its highest daily number since January — and another 48,000 on Sunday. However, deaths from the disease have stayed comparatively low. More than 128,000 people across the U.K. have died from the disease, the highest death toll in Europe.

About 67.8 percent of adults, or just over half the total population, have received two vaccine doses.

Despite repeated government reassurances about the vaccine rollout, medical experts have warned that "Freedom Day" could be a threat to the rest of the world.

More than 1,200 scientists backed a letter in the British medical journal The Lancet criticizing the government's decision while warning that the strategy could allow vaccine-resistant variants to develop.

Whitty also warned that the number of people hospitalized with Covid-19 could hit "quite scary" levels.

"I don't think we should underestimate the fact that we could get into trouble again surprisingly fast," he said Thursday during a webinar hosted by the Science Museum.

Families of many of those who have died from Covid-19 in Britain also criticized the government's plan.

"The overwhelming scientific consensus is that lifting restrictions on Monday will be disastrous, and bereaved families know firsthand how tragic the consequences of unlocking too early can be," Jo Goodman, a co-founder of Covid-19 Bereaved Families for Justice, told Reuters.

"There is a real fear that once again the government's thinking is being driven by what's popular rather than the interests of the country," he said.

The Associated Press and Reuters contributed.