Who would be a central banker these days? Time was when nobody much knew or cared about those strange greybeards who talked gobbledygook about monetary aggregates and output gaps. They toiled away in happy obscurity for decades, like Santa’s elves, always happy to let somebody else take the credit for their hard work, measuring their success by their anonymity.

In the 1980s we suddenly realised they ruled the world. Paul Volcker at the US Federal Reserve and a succession of stern Germans at the Bundesbank became front-page news for their unbending efforts to get inflation under control.

In the heady days of the 1990s, they went from newsmakers to cult leaders. Alan Greenspan replaced Eric Clapton as God. The unwieldy creature known as the European Central Bank took flight. And Gordon Brown, then in happier, more innocent times, freed the Bank of England from the shackles of political control.

Now these men and women who set our interest rates and keep our financial systems functioning must wish they were obscure again. Having run monetary policy at the Bank for the best part of a decade with a competence that ought to make Mr Brown blush, Mervyn King finds himself loaded on to the tumbril. His handling of the Northern Rock fiasco was surely less than perfect, but did it really merit the opprobrium now heaped on him?

I am told by someone close to him that he feels his isolation following the debacle very keenly. It is so bad, he says, that his friends do not return his phone calls any more. I think we can guess the identity of some of those “friends”.

Over here in the US, things have not got that bad for the Federal Reserve. Ben Bernanke, the Fed Chairman, can presumably still pick up the phone to anyone in the world and find an attentive ear.

Yet as the storm clouds darken on the American economic horizon, the central bank knows that it, too, is at risk of becoming carrion for the vultures who scavenge the byways of electoral politics. Though recessions are natural economic events, as inevitable as death and taxes, the Fed will surely get the blame if the United States has one in 2008, a presidential election year.

Last week the economic danger signs flashed bright red. Growth in the third quarter of 2007 was almost 5 per cent at an annual rate, but the data for this quarter suggest that momentum has virtually ground to a halt. The housing market continues to contract at alarming levels. The Government reported last Friday that personal consumption spending was static in October.

All this is deeply awkward for the Fed. You will recall that at the last meeting of its monetary policy setting committee on Hallowe’en, the central bank cut interest rates by a quarter-point, but issued a strong warning to markets not to expect any more. The risks to the economy were, it said, evenly balanced now between inflation and a slowdown.

Last week - only four weeks later - the Fed was forced to retract. Increasingly concerned that the Fed was starting to look like Nero while the economy blazed beneath it, Donald Kohn, the sagacious vice-chairman whose antennae are as well-tuned as those of any central banker, decided he had better change the fiddle’s tune. The deteriorating conditions in financial markets in recent weeks, he said, had changed the economic outlook for the worse.

Two days later Mr Bernanke followed up with similar language and conversations with senior officials confirm to me that the fix is now pencilled in. The Fed will cut rates at its meeting next week - and may do so again in the new year.

All this casts a cloud over the Fed’s judgment. It makes the central bank look hostage to events in a way that cannot help but undermine confidence in it. It is true that financial conditions clearly have changed in the past month, but this is the second time in less than four months that the Fed has had to turn on a dime. In August, when the financial crisis first broke, the Fed initially was slow to acknowledge its severity.

Ironically, Mr Bernanke’s performance is also hampered by his own laudable efforts to run monetary policy more openly.

Under Mr Greenspan, policymakers tended to follow the chairman’s lead. The Bernanke Fed is more collegial. Participants agree that there is more debate these days, but the downside is that you don’t always get consensus and it becomes harder for the chairman to “promise” policy moves in advance of the meeting where the decision is made.

In these trying times, we want our revered central bankers to demonstrate two perhaps contradictory qualities: nimbleness and clarity. The Fed has done well with the first so far, but perhaps at the expense of the second.

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