However, Mr. Carney argued that his policy “is working” and had instilled business confidence by giving more certainty, helping growth prospects. Even critics of forward guidance had not predicted such a sharp fall in unemployment, he said, while admitting that the central bank had learned from its experience.

The speed with which the central bank has had to change strategy raises some awkward questions about its credibility nonetheless. The policy was introduced with much fanfare by Mr. Carney as he took over as Bank of England governor in the summer, when the unemployment rate was 7.8 percent and Britain’s economy was in much need of support.

Some economists have said the policy lacked credibility from the start because the unemployment rate threshold was too high, leaving investors and consumers wondering about how soon interest rates would rise again.

Robert Wood, an economist at Berenberg bank in London, welcomed Wednesday’s move, which he said was “an abrupt U-turn” and marked a return to “inflation targeting, with a few bells and whistles attached.”

The bank said inflation had returned to its 2 percent target and suggested it would remain under control during the next three years.

The pound jumped on Wednesday, suggesting that financial markets were factoring in a rate increase in 2015 despite Mr. Carney’s comments. Brian Hilliard, chief economist for Britain at Société Générale in London, said the Bank of England might see the positive side of a rise in the value of sterling, which would help reduce inflation.

But he added that the bank would be disappointed that the markets had not believed that interest rates would stay low for some time. Mr. Carney’s updated forward guidance gave “no firm message,” Mr. Hilliard said.