Sally Dewar, the managing director of risk at the UK Financial Services Authority, will leave the regulator in May 2011, becoming the second senior official this year to announce plans to depart.
Ms Dewar, 41, who has been at the FSA for eight years, said she had decided not to seek to replace Hector Sants as head of the agency. She is responsible for market supervision, clearing and settlement as well as identifying and mitigating risk at financial services firms.
"Dewar's departure in May 2011 is interesting and surprising news," said Michael McKee, a partner in the law firm DLA Piper's financial services regulatory group. "Uncertainty surrounds the future of the FSA and its leadership and the resignation of Sally – considered by many to be a front-runner to replace Hector Sants – will only increase this."
Mr Sants, the FSA's chief executive, said in February he would step down this year. The agency, which may be split up or made to report to the Bank of England by the UK's coalition government, has beefed up regulation following complaints it did little to detect the financial crisis.
Ms Dewar became a managing director at the FSA in January 2008. She worked in the LSE's company listings department from 1998, when the exchange still oversaw the business. From 2002 to 2005 she was head of the UK Listing Authority at the FSA. bloomberg