Fifteen hours after she was taken out of an ambulance at Queen’s Hospital with chest pains and pneumonia, Marian Patten was still in the emergency room, waiting for a bed in a ward. Mrs. Patten, 78, was luckier than others who arrived at this teeming hospital, east of London: She had not yet been wheeled into a hallway.

For months, doctors at Queen’s have been forced to treat people in a corridor because of a lack of space. As the ambulances kept pulling up outside, the doctor supervising the E.R., Darryl Wood, said it was only a matter of time before nurses would begin diverting patients into the overflow space again.

“We’re in that mode every day now because the N.H.S. doesn’t have the capacity to deal with all the patients,” Dr. Wood said.

Despite her ordeal, Mrs. Patten was sympathetic. Decades ago, she said, the National Health Service saved her husband’s life when he had a heart attack. “It’s got to cope with a lot more people,” she said. “You can’t be grumpy about it.”

Her stoicism captures the reverence that Britons have for their cradle-to-grave health system, but also their rueful sense that it is broken.

As it turns 75 this month, the N.H.S., a proud symbol of Britain’s welfare state, is in the deepest crisis of its history: flooded by aging, enfeebled patients; starved of investment in equipment and facilities; and understaffed by doctors and nurses, many of whom are so burned out that they are either joining strikes or leaving for jobs abroad.

Interviews over three months with doctors, nurses, patients, hospital administrators, and medical analysts depict a system so profoundly troubled that some experts warn that the health service is at risk of collapse.

“Doctors and nurses face an endless stream of patients filling beds,” said Matthew Trainer, the chief executive of the N.H.S. trust that runs Queen’s and another nearby hospital, the King George. “For the clinical staff, that removes a sense of hope — that sense that what you’re doing matters.”

More than 7.4 million people in England are waiting for medical procedures, everything from hip replacements to cancer surgery. That is up from 4.1 million before the coronavirus pandemic began in 2020.

Mortality data, exacerbated by long wait times, paints a bleak picture. In 2022, the number of excess deaths rose to one of the highest levels in the last 50 years, and those numbers have kept rising, even as the pandemic has ebbed.

In the first quarter of 2023, more than half of excess deaths — that is, deaths above the five-year average mortality rate, before the pandemic — were caused by something other than Covid-19. Cardiovascular-related fatalities, which can be linked to delays in treatment, were up particularly sharply, according to Stuart McDonald, an expert on mortality data at LCP, a London-based pension and investment advisory firm.

Proliferating labor unrest only adds to the crisis, throwing hospitals that were already barely coping into near paralysis. While Mrs. Patten waited for a bed at Queen’s, doctors were picketing outside, protesting starting wages that are comparable to those earned by baristas working at Pret-a-Manger, a sandwich chain in the hospital’s lobby.

Seeking to solve the problem, Prime Minister Rishi Sunak last month announced a 15-year plan to recruit and train 300,000 nurses and doctors, budgeting 2.4 billion pounds (about $3 billion) for the first five years. But critics point out that the plan does not fund wage increases, the only surefire way to prevent workers from leaving.

The fate of the N.H.S. matters beyond Britain. Spiraling health care costs are bleeding public finances in almost every country, regardless of their political systems. The N.H.S. has always managed to deliver a level of care that justified its giant footprint in British public life, and it is hard to imagine a vibrant Britain if the service is not stabilized.

Politically, however, Britain’s fiscal austerity exacerbated the system’s failings. Covid exposed a legion of problems — including poor management and corroded facilities — that had been incubating inside the service since Conservative-led governments began curbing budget increases in 2010.

Health care spending rose by an average of less than 2 percent a year from 2010 to 2019, compared with 5.1 percent from 1998 to 2008. Britain spent less a year per person on health care than the wealthiest European Union countries during the decade of austerity, and now has fewer doctors and hospital beds per capita than its European neighbors. Its capital investment lagged the bloc’s average by $41 billion, according to the Health Foundation, which tracks the industry.

That has led to horror stories like doctors in a hospital outside London discovering dirty water from a leaky pipe in the ceiling dripping onto a circuit board that controls high-tech surgical equipment.

“Austerity has made matters a lot worse,” said Nigel Edwards, the chief executive of Nuffield Trust, a health research organization. “There’s been lots of salami-slice savings over the years, which has made the system much more fragile.”

No mainstream politician proposes to privatize the N.H.S.: The specter of the inequitable U.S. health system still horrifies many Britons. And in some ways, the service remains a marvel, one of the world’s most comprehensive, taxpayer-funded health care providers — “free at the point of delivery,” in the words of its utopian motto. It still offers annual physical exams, mammograms, vaccinations and other services at a level that visiting Americans find impressive.

Indeed, jaundiced observers say the N.H.S. is perpetually in crisis. But this time, the problems are of a different order, magnified by Britain’s faltering economy and its convulsive, post-Brexit politics. Experts say its model of universal access has become unsustainable, and there is no clear blueprint to reinvent it.

These problems are compounded by a breakdown in primary care, which has made it all but impossible for many people to get an appointment with their family doctor. With a shortage of general practitioners and nowhere else to turn, the E.R. has become the first stop for millions of sick Britons.

The interconnected nature of the N.H.S.’s problems — financing, staffing, case load, efficiency — makes simple fixes impossible. And because of its hallowed status as a national treasure, any efforts at root-and-branch change quickly run up against political resistance.

“It has become this albatross around our necks,” said Sally Davies, the master of Trinity College at Cambridge University, who served as the chief medical officer of England from 2010 to 2019. “You tinker with it at your peril.”

“The N.H.S. became the nation’s religion,” she added, “but it’s actually a National Sickness Service.”

With Dolly Parton’s office-worker anthem “Nine to Five” squawking from a speaker, a group of young doctors rallied next to a traffic circle outside Queen’s Hospital. They brandished banners that said, “£14/hour is not a fair wage for a junior doctor,” and waved at motorists, some of whom honked as they drove past.

It was mid-March, the first three-day walkout of a labor action that shows no sign of being resolved (a five-day strike, their longest yet, began on Thursday). The junior doctors — qualified physicians who are still in clinical training — have been seeking a 35 percent wage hike, which they say is needed to counteract a more than 25 percent cut in real wages since 2008.

In this season of strikes, the junior medics have been joined by senior doctors, nurses and ambulance workers. They all list the same grievances: long hours, relentless pressure and pay that has failed to keep pace with months of double-digit inflation.

With junior doctors striking, Queen’s pressed more experienced physicians to replace them, resulting in quicker diagnoses that briefly reduced E.R. waiting times. Reassigning the doctors came at a cost to other treatment, however. The hospital was forced to cancel 495 surgeries and 4,731 outpatient appointments.

“It looks like we’re coping,” said Mr. Trainer, the chief executive of the hospital trust, “but it’s a bit like the Tube system coping by closing a third of its lines.”

With more than 700 beds, Queen’s serves 800,000 people in three ethnically diverse boroughs that sprawl northeast of London. Though only 17 years old, the hospital, with its four squat circular brick buildings, already looks as tired as its staff.

Beyond the immediate crisis, Mr. Trainer said, the N.H.S. risks losing the next generation of doctors and nurses.

Max Berrill, 32, a trainee in internal medicine, said he and his colleagues routinely pulled 12-hour shifts, answering phones that rang every 10 seconds and treating frustrated patients.

Facing a decade of training in those conditions, some of his friends were abandoning the N.H.S. for jobs in Australia or New Zealand, he said. That exodus is an acute problem for a service that was already plugging a shortage by recruiting doctors from abroad, and it is not limited to the N.H.S.

The number of full-time general practitioners in England has declined steadily in recent years. If current trends continue, there will be a shortfall of about 8,800 family doctors by 2031, according to the Health Foundation.

“Nearly everyone loves the part of the job that involves treating patients,” said Dr. Berrill, taking a break from his roadside protest. “But the system has thrown up so many barriers to prevent you from doing that.”

During the darkest days of the pandemic, people gathered once a week to cheer and bang metal pots for the N.H.S. Children colored “Thank you N.H.S.” signs that were placed in the windows of 10 Downing Street. Boris Johnson, the former prime minister who was treated for Covid at an N.H.S. hospital, was among those who turned out to clap.

Protecting the health service has become an article of faith for British leaders of all parties. Mr. Sunak, who has made shorter wait times one of the five bedrock goals of his government, regularly reminds Britons that his father was a physician and his mother a pharmacist.

“When I talk about the N.H.S.,” he said in January, “I’m not just talking about a prized public service, I’m talking about my family’s life calling.”

Such devotion was not inevitable. In the service’s early decades, Britons were wary of public health care, fearing it would meddle in their relationships with their family doctors. Those suspicions crested in the 1980s with the free-market revolution of Margaret Thatcher.

Yet rather than being privatized, the N.H.S. survived the Thatcher years. That was partly because its defenders shrewdly contrasted it with health care in the United States, playing up America’s soaring costs, deep inequities and vast number of uninsured.

But more important, the champions of the N.H.S., in research institutes, academia and the news media, developed a multiyear public-relations campaign that transformed the service into a quasi-sacred institution, so revered that its birthday was celebrated with a service at Westminster Abbey.

“They deliberately plugged it into British national identity,” said Andrew Seaton, a historian at Oxford University who has just published a book, “Our N.H.S.: A History of Britain’s Best-Loved Institution.” “It involved this cultural dynamic, making the N.H.S. seem integral to British culture.”

That triumph of marketing has created a predicament for politicians: They feel forced to be cheerleaders for a system that is eroding before their eyes, yet the most obvious solution — throwing piles of money at it — is no longer economically feasible in an era of ballooning budget deficits.

Experts periodically float ideas like privatizing parts of the service or charging fees for some treatments, which might make people less quick to go to the E.R. for minor health issues. Sajid Javid, a Conservative former health secretary, has proposed changing its funding base from taxes to an insurance-based system, like that used in Germany.

But Mr. Edwards of the Nuffield Trust said there was little evidence that the service’s problems stemmed from how it was funded. Other high-income countries have had woes with their health systems.

“I doubt there will be an appetite for changing the funding model or changing the ownership of the hospitals,” Mr. Edwards said. “The risk, then, is they try to play with the train set, which is what incoming governments like to do.”

For all of the doom-saying about the N.H.S., there are things that still work, like the physicals and mammograms. And the hospitals themselves are experimenting with new ways to treat patients more efficiently to shorten waiting times.

That kind of adaptation is taking place at Queen’s, where Mr. Trainer pointed to some hard-won gains — or, as he calls them, “green shoots.” The percentage of patients with serious illnesses or injuries who are treated within four hours of being admitted increased from its low point of 30 percent in February to 48 percent in May, its best performance since August 2019.

That is largely thanks to a new same-day emergency care unit in the E.R. Intended for people with less serious issues, it allows the hospital to discharge more patients without having to get them a bed.

At the King George, the smaller sister hospital of Queen’s, Gerald Merritt, a retired bus driver, was patient as doctors prepped him for a knee replacement one morning. He had waited six months for the operation, but that was two months less than he waited to have his other knee replaced in 2018.

“Everybody would love to have it done tomorrow,” said Mr. Merritt, 69, who attributed his failing knees to a lifetime of rock climbing and hill walking. “But you’re prepared to put up with a wait.”

An hour later, Mr. Merritt, under a spinal anesthetic, chatted amiably with a doctor, while on the other side of a curtain an orthopedic surgeon drilled into his knee. He is one of about 500 people who will get knee and hip replacements this year, a high volume that is possible only because the surgery unit is walled off from E.R. patients that clog the operating rooms at Queen’s.

That level of improvement shows that adjustments on the fly can produce a quick fix, but there is usually another problem waiting around the corner. At the King George, doctors cannot discharge patients quickly enough because there is nowhere to send them for longer-term therapy.

That is yet another weak link in the chain — and one that is out of its control. In Britain, local councils, not the National Health Service, are responsible for social care. Years of budget cuts have left them stretched and not up to the task.

Given the need to overhaul primary care and social care, some experts argue the best thing the N.H.S. can do is simply run its hospitals better. At Queen’s, even with the recent improvements, patients suffering from mental health issues can be stranded in the emergency room for more than 36 hours.

“Forget about big ideas, like ‘let’s introduce fees,’ and focus on the basics,” Mr. Edwards said. “You can ensure they’ve got functioning computers so they don’t spend 15 minutes logging on.”

In the E.R. at Queen’s, nobody had the luxury to ponder long-term fixes. In one bed, Michelle Scanlan, 54, was waiting to be treated for a gash on her face from falling on a glass coffee table. Next door, Kaushik Bhatt, 67, was waiting for a bed after feeling faint because of low blood sugar.

In the resuscitation unit, which handles the most unstable patients, Dr. Wood, the E.R. doctor, took a break after checking on Tony Eaton, 48, a worker on the London Underground who was recovering from a hypoglycemia attack.

It was a comparatively peaceful moment in a job that rarely has them, and Dr. Wood was in a reflective mood.

“I come from South Africa, where it’s tough and we see a lot of trauma,” he said, after pausing to pick up a ringing phone. “But it doesn’t compare to this. There’s just too much that’s hitting us.”