Britons Love the N.H.S. Some Will Also Pay to Avoid It.

For David Haselgrove, it was a battle each day to get out of bed, then another struggle to put on his socks. Stairs were often impossible, and the pain made him tetchy and difficult to live with.

But when he sought medical help for his arthritis, Mr. Haselgrove was told the wait for a specialist consultation was more than two years. It might be another two years before surgery.

“If I wasn’t the person I am, I would have been losing the will to live because the pain takes over your life,” said Mr. Haselgrove, 71, who is now fully mobile after a successful hip replacement.

His recovery has nothing to do with Britain’s National Health Service.

Instead, Mr. Haselgrove, who ran several small businesses during his working life, flew to a clinic in Lithuania to have surgery, becoming one of a growing number of Britons who have dipped into their own pockets to pay for procedures to which they are entitled free on the N.H.S.

Free, universal health care — funded from general taxation and payroll deductions — is the founding principle of the National Health Service, one of Britain’s most revered institutions and the most enduring part of the welfare state that the country set out to build after the suffering of World War II.

But it is a promise that takes ever longer to fulfill.

After the financial crisis, the Conservative-led coalition government, elected in 2010, embarked on a period of austerity during which health spending failed to keep pace with the needs of an aging population.

In the decade leading up to the coronavirus pandemic, spending in real terms increased just 0.4 percent per person, per year — including four years in which spending per person actually fell, according to the Nuffield Trust, a research institute that specializes in health. Investment in buildings and equipment, including in vital diagnostic tools such as CT and M.R.I. scanners, has significantly lagged medical systems in other advanced economies, according to the King’s Fund, a health-focused think tank.

That contributed to a backlog of 4.6 million procedures even before the pandemic, a number that swelled to six million as planned procedures made way for emergency care during the Covid crisis. The line for treatment has only grown since. It is now about 7.7 million procedures, representing about a 10th of the population. Thousands have waited more than two years, often in pain.

Little wonder, then, that many Britons who can afford to pay to cut the line are doing so, while some of more limited means are dipping into savings or taking on debt. Yet that trend, some critics say, could undermine a health care system that has been a bedrock of British life for three-quarters of a century.

Private medical insurance is costly in Britain, and taxable when offered as a benefit by employers, so the shift is most visible when people pay for operations and other medical help out of pocket.

According to the Private Healthcare Information Network, which publishes data on the sector, there were about 50,000 “self-pay” medical admissions in a typical quarter before the pandemic. That figure is now steadily substantially higher; in the first quarter of this year, it was 71,000, close to a record.

That does not include patients who go overseas, like Mr. Haselgrove. At 7,000 euros, about $7,500, a hip replacement at the Nord Clinic in Lithuania was significantly cheaper than it would have been in a private hospital in Britain.

Joint replacements like Mr. Haselgrove’s “have the longest waiting times in the country,” said Deborah Alsina, the chief executive of Versus Arthritis, a charity. “As a result, we are increasingly hearing from people who are paying to have their hip or knee replaced privately, in a fraction of the time they’d be waiting on the N.H.S.”

Some critics of private involvement in British health care question whether for-profit providers are truly increasing the system’s capacity. Britain is chronically short of health workers, with over 100,000 N.H.S. positions vacant. Most specialists who work in both systems spend the vast majority of their time on N.H.S. cases, data suggests. But private health care providers do rely on coaxing additional work from thousands of surgeons and other senior doctors whose primary employer is the N.H.S.

And when a routine private operation becomes an emergency, it is often the public system that has to respond, because many private hospitals do not have emergency or intensive care departments.

But the deepest risk of the rise in self-pay patients, according to Chris Thomas, principal health fellow at the Institute for Public Policy Research, a progressive think tank, is not to the health service’s operations, but to its political underpinnings.

The British health system, he said, is built around the idea of “universalizing the best” — creating a system “as good for a rich person” as for a poor one, Mr. Thomas said.

If wealthier people increasingly opt out, Mr. Thomas said, the N.H.S. will become a second-class system for those who cannot afford to do so, resulting in “a slow erosion of support.”

Some right-wing politicians have begun calling for a structural rethink — not a new idea but one with previously limited support even among free-market enthusiasts in the Conservative Party. The explosion in waiting list numbers has helped to fuel calls for change.

Mr. Javid is planning to leave Parliament at the next election, however, and Conservatives still running for office, along with the representatives of every other mainstream party in Britain, almost universally present themselves as champions of the N.H.S.

For now, even Britons who pay for care often do so reluctantly — sometimes feeling guilt at jumping the line — while arguing for a more generously funded public system.

Romy Cerratti, 43, a mental-health campaigner who lives in Buckinghamshire, north of London, has paid both for surgery — to remove painful breast implants she was given two decades ago as part of an N.H.S. operation to correct a congenital abnormality of the breast bone — and for psychotherapy. She fears she may need a further operation and is still awaiting N.H.S. group therapy after more than two years on a waiting list.

When she discusses health care with friends, she said, most tend to rally behind the N.H.S. “People say, ‘You don’t want to be like America — it’s a two-tier system,’” Ms. Cerratti said. She was able to pay for the surgery cost of 7,000 pounds, about $8,800, because of an inheritance, but has had to cut back on private therapy for financial reasons.

“I always say we’ve got a two-tier system here at the moment because essentially those that can afford to go private are getting decent care,” she noted.

For those who cannot, she added, “It’s very much a question of luck.”