"You could just feel it. The pent-up demand. It was like a jack-in-a-box. It just went pop! And everyone went berserk," Tristan Moffat, operations director of the club, told The Washington Post.
"You could sing. You could dance," activities that have been "forbidden" since March 2020, he said. "I've been in this business for 21 years, and I've never seen anything like it. It was electric. It was buzzing."
And the masks? Moffat estimated that three-quarters of the 300 clubgoers in the converted Victorian warehouse in the Farringdon neighborhood took their face coverings off.
It's now their legal right.
On Monday, almost all remaining coronavirus restrictions in England were lifted. Scotland, Wales and Northern Ireland are still maintaining some measures, at least in the near term.
Also on Monday, the U.S. Centers for Disease Control and Prevention raised its covid-19 risk assessment for Britain to the highest level, and the State Department issued a do-not-travel advisory.
The changes reflect an exponential rise in coronavirus cases, propelled by the highly contagious delta variant. The United Kingdom reported 48,161 new coronavirus cases on Sunday. In a few days, the caseload could match January's peak.
This time, however, there are far fewer deaths and hospitalizations. And Johnson's government is convinced that the country's inoculation campaign - with 68.5 percent of Britain's adult population fully vaccinated - will protect the population and the National Health Service (NHS).
"It is right to proceed cautiously in the way that we are," Johnson said at a Monday news conference, "but it is also right to recognize that this pandemic is far from over."
He urged nightclubs to check people's NHS covid passes, which provide proof of vaccination, recent testing or immunity after having recovered from the virus. And he said that, starting the end of September, those who aren't fully vaccinated won't be allowed entry into nightclubs or other crowded venues.
Johnson, who is vaccinated, is in quarantine after being in contact with an infected individual - none other than his health secretary.
The British government denies that it is trying to hasten the arrival of "herd immunity" - the point where the virus has no place to go because the percentage of people vaccinated or protected by past infection breaks the chain of the contagion.
But many scientists say that this is essentially what the policy implies. Some health experts have called it a reckless experiment with dangerous consequences for the world. Others say it is reasonable.
In England, concert halls, theaters, sports arenas, nightclubs and other entertainment venues are now allowed to open with no capacity limits.
Want to get married? Or attend a funeral? Go ahead. Invite as many people as you want. The government is also urging workers to return to their offices.
There are no more legal requirements to wear masks - although there is plenty of confusion. The government said it "expects and recommends" that masks be worn in crowded and enclosed places, and some shops and businesses are asking customers to don the face coverings.
At Waterloo station, a major transport hub in central London, mask guidance depends on where exactly a person is standing. In the subway area of the station, people are still supposed to mask up. But in the train station, masks are only encouraged, according to the signs, "out of respect to others."
On Monday, Pat Price, 79, was wearing a blue mask and sitting in the train station next to her husband, Tony Price, 75, who was not wearing a mask.
Pat, who is fully vaccinated, said she always wears a mask when she's out, adding, "The majority of people are quite happy wearing a mask." She said she welcomed "Freedom Day."
"They have got to open up; you can't keep shutting it down," she said. "I don't think we can be mollycoddled to live in a bubble the whole time."
Tony Price said he took off his mask to sit and read the paper. "I have had it on all morning," he said. "I don't like wearing a mask, but I still will. . . . I think now it should be up to the individual. I agreed in the past when it was mandatory. But we have to look to the future and getting back to normal, and normal isn't that."
Tony Carter, 39, a chef sitting on a bench at Waterloo station, said now that mask-wearing isn't mandatory, it puts vulnerable people at risk.
He said he wears a mask all the time, even at work, where his restaurant's rules state that it is mandatory only if more than four people are in the kitchen.
"It's got to be done until we can at least get cases down," he said of mask-wearing. "If cases can stay down, by all means take the masks off, and then it can be a proper Freedom Day. Until then, it's not really freedom."
Outside, thousands of anti-shutdown protesters gathered near Parliament, holding signs that read, "No to vaccine passports" and "Leave our DNA alone" and "Covid is a scam."
Megan Bullen, 25, an artist, said, "We are here today to stand for freedom."
Asked whether it wasn't, in fact, Freedom Day, she responded: "We don't think it's over yet. They are still mandating masks in supermarkets, people are still wearing masks, and they will try and roll out vaccines in September for the children."
She added: "We don't feel like it's freedom. It's a veil, and I think it's only a matter of time before we go back into lockdown."
The few people at the rally wearing masks, mostly reporters, were heckled and urged to uncover their faces.
England is already confronting a "pingdemic," with more than half a million people in a single week "pinged" by the NHS mobile phone app telling them to quarantine for 10 days because they had been in close physical contact with a person who tested positive. The guidance applies regardless of vaccination status, at least until Aug. 16, when the guidelines will change again.
More than 500,000 people were pinged last week. The number will probably increase this week, even as many people begin to delete the app from their phones.
Richard Walker, managing director of the Iceland Foods supermarket chain, told the BBC that his company has more than 1,000 people out - about 4 percent of the workforce - because they are quarantining after coronavirus exposure or isolating after a positive test. He said the company is hiring an additional 2,000 people "to give us a deeper pool of labor, because so many people are now getting pinged."
"A number of stores have had to close, and the concern is that as this thing rises exponentially, as we have just been hearing, it could get a lot worse, a lot quicker," he said.
For theater impresario Andrew Lloyd Webber, Freedom Day was anything but. For weeks, Lloyd Webber has been pledging to open his new musical, the $8.2 million "Cinderella," "come hell or high water." The show had been in socially distanced previews at the Gillian Lynne Theatre in London's West End.
In a post Monday on social media, he said he was forced to close the show after a member of the cast tested positive over the weekend. He called the government's isolation guidance a "blunt instrument."
"Cinderella was ready to go," he wrote. "My sadness for our cast and crew, our loyal audience and the industry I have been fighting for is impossible to put into words. Freedom Day has turned into closure day."