Sir John Gieve, the Deputy Governor of the Bank of England who was accused of lack of vigilance in the Northern Rock affair, is to stand down, it emerged last night.

Sir John was responsible for maintaining the stability of financial markets. His shock exit – he will officially leave next spring – upstaged Alistair Darling, the Chancellor, in his first Mansion House speech, in which he was simultaneously outlining plans to give the Bank of England an enhanced role in financial stability to try to prevent another banking collapse.

Sir John was appointed as one of the Bank’s two Deputy Governors in January 2006 and had 2½ years of his tenure left to serve. However, speculation about his future has swirled since last year, when he was savaged by the Commons Treasury Select Committee for not doing enough to prevent the crisis at Northern Rock.

It was not immediately clear last night whether Sir John was forced to resign or quit voluntarily. The Bank confirmed in a statement late last night that Sir John would step down next year. He said that it “makes sense for someone else to take on this task”, once the Bank’s new powers become enshrined in legislation.

His exit comes as the Bank faces its most difficult period for a generation. The Rock debacle and the Bank’s inability to tame resurgent inflation have led to increasing tensions with the Treasury.

It is unclear who will replace Sir John, but the Treasury has previously indicated that it would favour Paul Tucker, a former corporate financier and the Bank’s executive director in charge of markets, to take the role.

Mr Darling is also expected to confirm today that Charles Bean – the Bank’s chief economist – is to become its other Deputy Governor in charge of monetary policy. Mr Bean will succeed Rachel Lomax, who is standing down on July 1

Mervyn King, the Governor of the Bank, recently won a battle with the Treasury to have Mr Bean, his choice, appointed as Ms Lomax’s successor. The Treasury believed that the Bank’s management skills could become unbalanced, given Mr King’s background as a respected academic economist, with Ms Lomax and Sir John, both former Whitehall Permanent Secretaries, as his deputies.

The Conservatives and senior MPs had urged Mr Darling to appoint someone with clout in the City, rather than Mr Bean, as the next Deputy Governor. Sir John’s resignation will now enable Mr Darling to do exactly that.

The shake-up at the Bank emerged as Mr Darling used his Mansion House speech last night to unveil a new financial stability committee that will oversee the Governor’s actions and hold him accountable if potential banking crises are not averted. The committee will be staffed with members of the Bank’s Court and eminent City figures to be handpicked by Mr Darling.

“The aim is to hold Mervyn accountable for his actions,” an insider said yesterday.

Mr Darling has made clear he was disappointed by the Bank’s performance in its financial stability role last year as the credit crisis took hold and banks began clamouring for help. To avoid a repetition of the crisis, the Chancellor said the Government would give the Bank “formal legal responsibilty” for financial stability, alongside its monetary policy role.

The measures are part of the Treasury’s banking reform Bill, first laid out at the beginning of the year. Mr Darling said that he would give more details of the committee today in a letter to John McFall, chairman of the Treasury Select Committee.

The Chancellor said he would also outline new powers for the Financial Services Authority to help to prevent the failure of a bank and to address market abuse and insider trading. “We must do everything possible to prevent problems, which could pose a wider threat to stability,” he said.

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