Serco said its Chief Executive Chris Hyman had resigned as it unveiled a restructure of the business and plans to beef up its board in a bid to rebuild its damaged relationship with the UK government. Hyman, who has stepped down with immediate effect, said it had become clear that the best way for the company to move forward was "for me to step back".His departure comes after the revelations in July that Serco and G4S had overcharged the government by tens of millions of pounds for electronically tagging criminals. The FTSE 250 global outsourcing group, which also provides support to the armed forces including the Royal Navy, announced it would split its British central government work into a separate unit from its activities in the wider public sector. Serco also said it planned to hire three more non-executives directors to the board, to set up a board committee for corporate responsibility and to strengthen its contract level governance and transparency. Alastair Lyons, Non-Executive Chairman, said: "The decisive and comprehensive actions we have set out today, alongside the programme already underway, should leave no-one in any doubt about how seriously Serco takes these issues and our commitment to rebuild the confidence of our UK Government customer."Hyman's shoes will be filled on a temporary basis by Ed Casey who has led Serco's American business since 2005. Serco plans to look outside of the business for Hyman's permanent successor and said the search had already begun.The financial terms of Hyman's departure will be sorted out "as soon as practicable", it said.Shares in Serco were up 1.72% at 562p at 12:12 on Friday. TB