LONDON -- The U.K. recorded more than 50,000 new coronavirus cases in one day Friday for the first time in six months, as the British government's top medical adviser warned that the number of people hospitalized with COVID-19 could hit “quite scary” levels within weeks.

Government figures showed another 51,870 confirmed lab cases, the highest number since mid-January. Infections have surged in recent weeks, mainly among unvaccinated younger people, as a result of the far more contagious delta variant and the easing of lockdown restrictions.

Despite the increase, the British government plans to lift all remaining legal restrictions on social contact in England on Monday and to ditch social distancing guidelines, as well as the legal requirement for people to wear masks in most indoor settings, including shops, trains, buses and subways.

The government is hoping that the rapid rollout of vaccines will keep a lid on the number of people becoming seriously ill with COVID-19 - a stance that some leading scientists at an emergency international summit critiqued as “reckless.”

The group, which includes advisers to the governments of Italy, New Zealand and Taiwan, said they joined forces through a “sense of urgency” to warn of the global consequences of allowing the delta variant to spread rapidly through the British population.

The scientists warned that the combination of high infections and high levels of vaccination “create the conditions in which an immune escape variant is most likely to emerge.”

One of the co-signatories to Friday's statement, Dr. William A. Haseltine of the New York-based think tank Access Health International, went further, describing the strategy as “murderous” and “unconscionable.”

Families representing many of those who have died from COVID-19 in the U.K. also joined in the criticism of the plan devised by Prime Minister Boris Johnson's Conservative government.

“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,” said Jo Goodman, co-founder of Covid-19 Bereaved Families for Justice. “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.”

Other parts of the U.K. - Scotland, Wales and Northern Ireland - are taking more cautious steps out of lockdown.

So far, the number of people in U.K. hospitals with virus-related illnesses and subsequently dying remains relatively low, certainly when compared with the peak of the second wave of the pandemic earlier this year.

But with the government putting the country on notice that daily infections could rise to over 100,000 this summer, concerns are clearly growing. Johnson has sought to rein in any euphoria around Monday's lifting of restrictions, an occasion tagged “Freedom Day” on social media.

Johnson is urging people to remain vigilant when meeting with others and to carry on wearing masks in enclosed or crowded places.

His chief medical officer, Chris Whitty, told a webinar hosted by London's Science Museum late Thursday that the U.K. is “not out of the woods yet.”

“I don't think we should underestimate the fact that we could get into trouble again surprisingly fast,” Whitty said.

More cases will inevitably lead to more people requiring hospital attention even though the vaccine rollout has helped build a wall of immunity around those deemed the most vulnerable. More than two-thirds of British adults have received both doses of a vaccine, and almost 88% have had one dose.

Friday's government data showed 3,964 people hospitalized with COVID-19, the most since late March. Though the number has gone up steadily in recent weeks, it remains far lower than in January, when British hospitals had around 40,000 COVID-19 patients.

Alongside the increase in hospitalizations, daily virus-related deaths have risen to levels not seen since March. Another 49 virus-related deaths were recorded Friday, taking the U.K.'s total to 128,642, the seventh-highest in the world.

Whitty warned that the number of hospitalized COVID-19 patients is doubling about every three weeks and could reach “quite scary numbers” if the current trend continues.

“We are not by any means out of the woods yet on this. We are in much better shape due to the vaccine program, and drugs and a variety of other things,” he said.

“But this has got a long way to run in the U.K., and it's got even further to run globally,” he added.