John Kingman, the chief executive of UKFI, the body controlling the government's stake in Royal Bank of Scotland and Lloyds, has surprised the City and stunned the government by handing in his resignation. Kingman, a former Treasury official who played a key part in last year's part-nationalisation of RBS and Lloyd's, will leave once a replacement is found, UKFI said. "I have tremendously enjoyed leading UKFI over the last year and think the organisation is now very well placed to deliver its mission of protecting and creating value for the taxpayer," added Kingman.Reports today suggested Kingman, up to now a career civil servant, will move to a job in the private sector. His resignation coincided with the appointment of Sir David Cooksey as the new chairman of the quango. Opposition parties leapt on Kingman's departure as further evidence that the government's strategy for disposing of its stakes in the part-nationalised banks is in disarray."What is worrying about these changes is that Mr Kingman is leaving at a time when it's clear the Government hasn't really got a grip on the banks. He is the one person within the Treasury who knew where all the skeletons are buried and what's going on. His departure at this time will leave a massive hole," Liberal democrat spokesman Vince Cable said. The reports suggested Kingman has been planning to leave for some time and may be concerned about his job prospects if the Conservatives win the next election. UKFI has already been fiercely criticised for agreeing to a £9.6m pay package for new Royal Bank of Scotland chief executive Stephen Hester.New chairman Cooksey will take over from acting chairman Glen Moreno on 1 August. Cooksey, who is currently chairman of London & Continental Railways and FTSE 100-listed ENRC, is also a former chairman of the Audit Commission. He will earn a flat fee of £100,000 per year. UKFI is responsible for the state's 70% stake in Royal Bank of Scotland, 43% stake in Lloyds and 100% holding in Northern Rock and Bradford & Bingley.