The British lockdown that is being eased on Monday is the nation’s third. But it was first aimed at containing a variant of the coronavirus — offering an early warning to the world of the threat posed by the evolution of the virus and the difficulties in trying to control this particular form.

When the variant, known as B.1.1.7, was first discovered late last year in the southeastern English county of Kent, much about it was a mystery.

It appeared to be more contagious, but to what degree? Was it more deadly? How far had it spread?

The picture is becoming clearer. The most recent estimates suggest it is about 60 percent more contagious than the original form of the virus, and significantly more deadly.

That same variant is now spreading across continental Europe, prompting governments like those of France and Italy to impose new national lockdowns. The variant has also added urgency to the vaccination campaign in the United States — which is getting doses into millions of arms every day but still might not be fast enough to avoid yet another wave.

The vaccines being used in many countries have shown to be effective against it.

Britain’s vaccination campaign was launched with an urgency dictated by the moment, prioritizing first doses to spread a degree of protection as quickly and widely as possible.

Even after the lockdown was put in place, the variant propelled the country’s daily fatality rates to levels not seen since the peak of the pandemic’s first wave in April.

On Friday, the number of people with Covid-19 on their death certificate was just shy of 150,000.

But another statistic now offers hope. Nearly 32 million people have been given at least one dose of a vaccine — roughly half the adult population.

Officials are confident the combined effects of the lockdown and mass vaccination will provide a wall of protection. But, as England’s chief medical officer Chris Witty warned, it is a “leaky wall.”

A large majority of people under the age of 50 have yet to be offered a jab. And with supplies constrained around the world, eligibility is unlikely to be expanded for weeks or more.

The once-routine act of visiting a clothes store or shoe merchant took on a new meaning for the first shoppers who made an early-morning pilgrimage to Oxford Street, London’s busiest retail road that in recent months has been a desolate stretch of boarded up shops and empty stores.

Outside Niketown, JD Sports and Foot Locker, crowds were lining up by 7 a.m. as groups of mostly young men waited in line for a chance to get their hands on new sneakers.

Julian Randall, a dedicated collector who has spent the last 15 years amassing sneakers, left his London home at 2 a.m. to be there. He said he preferred to buy in store, rather than online, where it was harder to find specific shoes at a reasonable price.

“It’s virtually impossible to hop online and buy the shoes online — you don’t even have a chance,” he said. “In this day and age, we are in a recession, and I don’t want to be paying resell prices for shoes. I want to buy retail.”

The shops have remained mostly shuttered since the week of Christmas, when nonessential stores were forced to close across the region, but elsewhere in England, the closures have been in place even longer after coronavirus cases surged.

Retailers hope that there will be a splurge in spending by people who have amassed a record amount of savings — nearly $250 billion according to government estimates, roughly 10 percent of the Britain’s gross domestic product.

But for many stores, it is too late.

The flagship store of the British retailer Topshop on Oxford Circus, once a destination for fashion-hungry young adults, permanently shut its doors after its parent company, Arcadia Group, filed for bankruptcy last year.

Plywood boards cover the front of Debenhams, another retail chain that floundered during the pandemic, its extensive window displays now bare. The two companies crumbled within days of one another, as the country bounced from one lockdown to the next and the pandemic hastened the end of British high-street brands that were already teetering on the edge.

But the shuttered windows stood alongside some hopeful signs. Plastered in big letters on the shop front of John Lewis, a British department store, there was a clear message: “Come on in London, brighter days are coming.”

(Even that retailer has struggled, and it has explored converting parts of its Oxford Street store into office space.)

For those stores that did reopen, coronavirus precautions seemed to be front of mind, at least as the day began. Bokara Begum wanted to be as safe as she could during her shopping outing to Primark, so she arrived as doors swung open to beat the crowd.

“It’s just after 7 a.m., so I took advantage of that and came out here early,” she said, two brown paper bags in tow. “I was a bit panicky, really — I thought there would be a massive queue.”

One man showed up in his robe. Another couple had made a two-hour trek from a neighboring county.

A little over a dozen patrons, shivering in the Arctic chill gripping England, stood at the ready as Nicholas Hair, owner of The Kentish Belle, counted the seconds until the clock ticked over to a minute past midnight.

“Ladies and gentlemen, take your seats!” he said to applause.

Then, for the first time in months, he poured and served a pint.

“I mean, I’ve not seen my friends like this together for so long,” said Ryan Osbourne, 22. “When we have an opportunity like today to bring my friends together, it’s incredible.”

Not all pubs will be allowed to reopen on Monday — only the estimated 15,000 with outdoor space, for outdoor service only. And most of those will open later in the day.

But Mr. Hair had secured a special license to open The Kentish Belle, a small pub specializing in artisanal beers in a quiet southeast London neighborhood, at the earliest possible opportunity.

He was circled by news crews as he prepared to open.

The past year had been “dreadful,” he said, adding that he had not been able to access government funding for the past two months. “There are a lot of businesses like this that won’t survive.”

Uma Nunn, 43, traveled from Surrey to attend the night’s festivities. “We just wanted to show our support,” she said.

Her husband, Benjamin Nunn, a beer writer who spent the last open day for pubs at The Kentish Belle, said he thought it only fitting to return for the first. “This is one of the big things in my life, beer and music,” he said. “Now to be able to get that started up again, it’s energizing, it’s exciting.”

“It’s the middle of he night but hey, hopefully this will never happen again,” he added.

For the past year, the British economy has yo-yoed with the government’s pandemic restrictions. On Monday, as shops, outdoor dining, gyms and hairdressers reopened across England, the next bounce began.

The pandemic has left Britain with deep economic wounds that have shattered historical records: the worst recession in three centuries and record levels of government borrowing outside wartime.

Last March and April, there was an economic slump unlike anything ever seen before when schools, workplaces and businesses abruptly shut. Then a summertime boom, when restrictions eased and the government helped usher people out of their homes with a popular meal-discount initiative called “Eat Out to Help Out.”

Beginning in the fall, a second wave of the pandemic stalled the recovery, though the economic impact wasn’t as severe as it had been last spring. Still, the government has spent about 344 billion pounds, or $471 billion, on its pandemic response. To pay for it, the government has borrowed a record sum and is planning the first increase in corporate taxes since 1974 to help rebalance its budget.

By the end of the year, the size of Britain’s economy will be back where it was at the end of 2019, the Bank of England predicts. “The economy is poised like a coiled spring,” Andy Haldane, the central bank’s chief economist said in February. “As its energies are released, the recovery should be one to remember after a year to forget.”

Even though a lot of retail spending has shifted online, reopening shop doors will make a huge difference to many businesses.

Daunt Books, a small chain of independent bookstores, was busy preparing to reopen for the past week, including offering a click-and-collect service in all of its stores. Throughout the lockdown, a skeleton crew “worked harder than they’ve ever worked before, just to keep a trickle” of revenue coming in from online and telephone orders, said Brett Wolstencroft, the bookseller’s manager.

“The worst moment for us was December,” Mr. Wolstencroft said, when shops were shut in large parts of the country beginning on Dec. 20. “Realizing you’re losing your last bit of Christmas is exceptionally tough.”

He says he is looking forward to having customers return to browse the shelves and talk to the sellers. “We’d sort of turned ourselves into a warehouse” during the lockdown, he said, “but that doesn’t work for a good bookshop.”

With the likes of pubs, hairdressers, cinemas and hotels shut for months on end, Brits have built up more than £180 billion in excess savings, according to government estimates. That money, once people can get out more, is expected to be the engine of this recovery — even though economists are debating how much of this windfall will end up in the tills of these businesses.

Monday is just one phase of the reopening. Pubs can serve customers only in outdoor seating areas, and less than half, about 15,000, have such facilities. Hotels will also remain closed for at least another month alongside indoor dining, museums and theaters. The next reopening phase is scheduled for May 17.

Over all, two-fifths of hospitality businesses have outside space, said Kate Nicholls, the chief executive of U.K. Hospitality, a trade group.

“Monday is a really positive start,” she said. “It helps us to get businesses gradually back open, get staff gradually back off furlough and build up toward the real reopening of hospitality that will be May 17.”