An urgent search is under way for a new Deputy Governor of the Bank of England after it emerged that Rachel Lomax will step down from the role in only six weeks' time.

It is understood that, despite attempts to persuade her to stay on, Ms Lomax decided to stick by past indications that she would serve only one five-year term. A search for a successor, ordered by Alistair Darling, is at an early stage, sources said.

The gap at the top of the Bank comes at an awkward time for the Chancellor, with fears over the outlook for the economy and with relations between the Bank and the Treasury strained by the Northern Rock debacle and the credit crunch.

Ms Lomax's successor will face big challenges in steering and explaining the Bank's interest-rate decisions. This task is likely to prove demanding after Mervyn King, the Governor, made clear last week that surging inflation was likely to scupper chances for any more than one more rate cut this year, despite faltering economic growth.

The appointment is sensitive for the Treasury, since both the Chancellor and the Prime Minister may want to avoid installing a monetary policy “hawk” who would reinforce the Bank's hard line at a time when ministers will be hoping for base rate cuts to bolster slowing growth. Ms Lomax generally has been part of the more doveish faction on the Bank's Monetary Policy Committee. However, the Treasury will also want to avoid any overt sign of seeking to influence the balance of power at the independent Bank. The appointment is made by the Queen on the advice of the Prime Minister, who is advised by the Chancellor, with some input by the Governor.

There are indications that the Treasury may prefer to leave a vacancy on the MPC while it secures the best candidate, rather than make a rushed appointment. However, Mr Darling will be conscious that such gaps have been criticised by the Commons Treasury Select Committee and others.

The selection of Ms Lomax, and of Sir John Gieve, the other Deputy Governor, who oversees the Bank's financial stability role, were controversial because both were former top civil servants. Their moves to the Bank sparked accusations from some quarters that Gordon Brown was installing pro-Treasury figures.

Mr King is said to be keen that Ms Lomax's successor should come from a market or economic background, rather than the Civil Service. However, the Treasury's task of finding a candidate with strong credentials as an economist and the necessary political and administrative skills will be tough.

Two internal Bank candidates with strong claims would be Charles Bean, the popular former London School of Economics professor seen as a top-flight economic brain, and Paul Tucker, the Bank's markets director, often tipped as a future Governor.

The search for a Deputy Governor comes as the Treasury is also seeking a new chairman for the Financial Services Authority, with Lord Turner of Ecchinswell, the former CBI Director-General, a front-runner for the post.

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