By Lawrence White LONDON (Reuters) - Barclays Plc is about to overhaul its back office operations under a restructuring to help it comply with new post-crisis rules forcing British banks to ring-fence their retail operations from their riskier business. It has formed a new company that will operate as a standalone unit providing support services to both of its two main operations when they are formally separated - retail and investment banking, the bank said. The ring-fencing rules seek to avoid a repeat of the 2008 crisis, when banks' bad bets threatened depositors' cash.