The Bank of England stepped in to save a critical market this week. Economists say it was necessary but also worry about the precedent.When the Bank of England announced last week that it would buy bonds in unlimited quantities in an effort to stabilize the market for U.K. government debt, economists agreed it was probably a necessary move to prevent a cataclysmic financial crisis.They also worried it could set a dangerous precedent.Central banks defend the financial stability of the nations in which they operate. In an era of highly leveraged and deeply interconnected markets, that means that they sometimes have to buy bonds or backstop lending to prevent a problem in one area from spiraling into a crisis that threatens the entire financial system.But that backstop role also means that if a government does something to generate a major shock, politicians can be fairly confident that the local central bank will step in to stem the fallout.Some economists say that is essentially what happened in the United Kingdom. Liz Truss, the new prime minister, proposed a huge package of tax cuts and spending during a period of already high inflation, when standard economic theory suggests governments should do the opposite. Markets reacted forcefully: Yields on long-term government debt shot up, and the value of the British pound fell sharply relative to the dollar and other major currencies.The Bank of England announced that it would buy long-term government debt “on whatever scale is necessary” to prevent a full-blown financial crisis. The move was particularly striking because the bank had been poised to begin selling its bond holdings — a plan that is now postponed — and has been raising interest rates in a bid to bring down inflation.Economists broadly agreed that the bank’s decision was the right one. The rapid rise in interest rates sent shock waves through financial markets and upended a typically sleepy corner of the pension fund industry, which, left unaddressed, could have carried severe consequences for millions of workers and retirees, destabilizing the country’s entire financial system.“You saw very substantial market dislocation,” said Lawrence H. Summers, a former U.S. Treasury Secretary who is now at Harvard. “It’s a recognized role of central banks to respond to that.”To some economists, that was exactly the problem: By shielding the U.K. government from the full consequences of its actions — both preventing citizens from feeling the painful aftereffects and keeping government borrowing costs from shooting higher — the policy demonstrated that central bankers stand ready to clean up messy fallout. That could make it easier for elected leaders around the world to take similar risks in the future.Those concerns eased somewhat on Monday when Ms. Truss partly backed down, reversing plans to abolish the top income tax rate of 45 percent on high earners.But she appears poised to go forward with the rest of her proposed tax cuts and spending programs, putting the Bank of England in a delicate spot.Rising Inflation in BritainInflation Slows Slightly: Consumer prices are still rising at about the fastest pace in 40 years, despite a small drop to 9.9 percent in August.Interest Rates: On Sept. 22, the Bank of England raised its key rate by another half a percentage point, to 2.25 percent, as it tries to keep high inflation from becoming embedded in the nation’s economy.Mortgage Market: The uptick in interest rates roiled Britain’s mortgage market, leaving many homeowners calculating their potential future mortgage payments with alarm.Investor Worries: The financial markets have been grumbling with unease about Britain’s economic outlook. The government plan to freeze energy bills and cut taxes is not easing concerns.The “partial U-turn” from Ms. Truss “still leaves the Bank of England with a set of near-impossible choices,” analysts at Evercore ISI wrote in a note to clients. “The only way to alleviate this is for the government to take much bigger steps to restore credibility — but there is little sign this is imminent.”There’s a reason that the interplay between monetary policy and politics in the United Kingdom is garnering so much attention. Central banks have for decades closely guarded their independence from politics. They set their policies to either stoke the economy or to slow it down based on what was necessary to achieve their goals — in most cases, low and stable inflation — free from the control of elected officials.The logic behind that insulation is simple. If central bankers had to listen to politicians, they might let price increases get out of control in exchange for faster short-term growth that would help the party in power.Now, that independence is being tested, and not just in the United Kingdom. Central banks around the world are raising interest rates to try to fight inflation, resulting in slower growth and making it harder for governments to borrow and spend. That is likely to lead to tension — if not outright conflict — between central bankers and elected leaders.It is already beginning. A United Nations agency on Monday warned that the Federal Reserve risked a global recession and significant harm in developing countries, for instance. But the United Kingdom’s example is stark because the elected government is carrying out policy that works against what the nation’s central bank is trying to achieve.“One always worries that actions like these can affect incentives going forward,” said Karen Dynan, a Harvard economist who served as a top official in the Treasury Department under President Obama. “It’s basic economics: People respond to incentives, and fiscal policymakers are people.”Part of the issue is that it is hard for central bankers to single-mindedly focus on controlling inflation in an era when financial markets are fragile and susceptible to disruption — including disruptions caused by elected governments.Before 2008, the Fed had never used mass long-term bond purchases to calm markets in its modern era. It has now used them twice in the span of 12 years. In addition to last week’s moves, the Bank of England also turned to mass bond purchases to calm markets in 2020.Bank of England officials have stressed that the policies they announced last week are a temporary response to an immediate crisis. The bank plans to buy long-dated bonds for less than two weeks and says it will not hold them longer than necessary. The Treasury, not the bank, will be responsible for any financial losses. The bank said it remained committed to fighting inflation, and some economists have speculated that it could raise rates even more aggressively in light of the government’s growth-stoking policies.If the bank is able to hold to that plan, it could mitigate economists’ concerns about the longer-run risks of the program. If interest rates rise again and it gets more expensive for the government to borrow, Ms. Truss will still need to grapple with the costs of her proposed programs, just without facing an imminent financial crisis.But some economists warn that the Bank of England may find the situation harder to extricate itself from than it hopes. It may turn out that the bank needs to keep buying bonds longer than expected, or that it cannot sell them without threatening another crisis. That could have the unintentional side effect of giving the British government a helping hand — and it could demonstrate that it is hard for a big central bank to remove support from its economy when the elected government wants to do the opposite.Liz Truss, Britain’s prime minister, will still need to grapple with the costs of her proposed programs, but she won’t be facing an imminent financial crisis because of the Bank of England’s actions.Alberto Pezzali/Associated PressMs. Truss’s policies — particularly before her partial reversal on Monday — would work directly against the bank’s efforts to cool growth, stoking demand through lower taxes and increased spending. The rapid rise in bond yields last week suggested that investors expected inflation to rise even further.Under ordinary circumstances, these conditions would lead the Bank of England to do even more to bring down the inflation it had already been fighting, raising interest rates more quickly or selling more of its bond holdings. Some analysts early last week expected the bank to announce an emergency rate increase. Instead, the brewing financial crisis forced the bank to do, in effect, the opposite, lowering borrowing costs by buying bonds.While lowering rates and stoking the economy was not the point — just a side effect — some economists warn that those actions risk setting a dangerous precedent in which central banks can only tighten policy to control inflation if their national governments cooperate and do not roil markets in a way that threatens financial stability. That situation puts politicians more in the driver’s seat when it comes to making economic policy.Guillaume Plantin, a French economist who has studied the interplay between central banks and governments, likened the dynamic to a game of chicken: To avoid a financial crisis, either Ms. Truss had to abandon her tax-cut plans, or the Bank of England had to set aside, at least temporarily, its efforts to raise borrowing costs. The result: “The Bank of England had to chicken out,” he said.Policymakers have known for decades that when the government steps in to rescue private companies or individuals, it can encourage them to repeat the same risky behavior in the future, a situation known as “moral hazard.” But in the private sector, there are steps governments can take to offset those risks — regulating banks to reduce the risk of collapse, for example, or wiping out shareholders if the government does need to step in to help.It is less clear what monetary policymakers can do to prevent the government itself from taking advantage of the safety net a central bank provides.“There is a moral hazard here: You are protecting some people from the full consequences of their actions,” said Donald Kohn, a former Fed vice chair and a former member of the Bank of England’s Financial Policy Committee, who agreed that it is necessary to intervene to prevent market dysfunction. “If you think about the entities that benefited from this, one was the chancellor of the Exchequer, the government.”Some forecasters have warned that other central banks might have to pull back on their own efforts to fight inflation to avoid destabilizing financial markets. Some investors are speculating that the Fed will have to end its policy of shrinking government bond holdings early or risk stirring market turmoil, for instance.Not all of those scenarios would necessarily raise the same concerns. In the United States, the Biden administration and the Fed are both focused on fighting inflation, so any reversal by the central bank would probably not look like bowing to pressure from the elected government.Still, the common thread is that financial stability issues could become a hurdle in the fight against inflation — especially where governments do not decide to go along with the push to rein in prices. And how worrying the British precedent proves will depend on whether the Bank of England is capable of backing away from bond buying quickly.“Is this just an exigent moment that they needed to respond to, or does it give the fiscal authority room to be irresponsible?” said Paul McCulley, an economist and the former managing director at the investment firm PIMCO. “The question is who blinks.”Joe Rennison More