A former colleague of Kweku Adoboli reported the ex-UBS trader for improper trading practices almost one year before he was arrested for having allegedly caused the largest unauthorised trading loss in UK history, a court has heard.

John Hughes, who worked alongside Adoboli on UBS's London-based ETF trading desk, told a jury at Southwark Crown Court yesterday that he reported his co-worker for exceeding his trading limit in December 2010.