Robin Southwell is one of the PM's most trusted business leaders. But there is one blot on his career. Corporate Jet Services, a company that lays on planes for the rich and famous, collapsed in 2007 – costing its main creditor, HBOS, about £100m (and helping to bring about the bank's state bailout, at vast expense to the taxpayer). Tom Harper asks what was HBOS doing lending so much money to such a small firm. And how is it that Mr Southwell and other directors of the firm ended up buying back CJS for a knock-down price?