UBS’s chief financial officer yesterday told a London court that employees at the Swiss bank had to spend a “significant amount of time” reassuring clients about the stability of the firm rather than doing business with them, following the discovery of a $2.3bn loss allegedly caused by unauthorised trading in September last year.

Tom Naratil, who spoke as a witness for the prosecution in the criminal trial of ex-UBS trader Kweku Adoboli via video-link from New York, said that the incident had "adversely" impacted the bank and its relationship with clients.