A UBS trader raised the issue of a “slush account” in an electronic chat with Kweku Adoboli months before he was arrested over allegations he lost the Swiss bank $2.3bn (£1.4bn), a London court heard yesterday. Appearing as a witness at Adoboli’s trial, Darren Bailey rejected as “ridiculous” an accusation by the accused former trader’s lawyer that he ran a hidden trading book that served as the template for Adoboli’s illicit “umbrella" account. Adoboli, 32, was arrested on 15 September 2011, and has pleaded not guilty to two charges of fraud and two of false accounting. The prosecution says he routinely exceeded his trading limits and booked fake trades into the accounts to mask his true positions. The trial continues.