Former UBS trader Kweku Adoboli was at one stage at risk of losing the Swiss bank nearly $12 billion (7.4 billion pounds) in unhedged investments, a British prosecutor said on Friday.

Adoboli, 32, has pleaded not guilty to two counts of fraud and two counts of false accounting related to $2.3 billion in losses uncovered a year ago.

"He had been sucked into the gambler's mindset and he started throwing good money after bad," prosecuting counsel Sasha Wass told the jury at Southwark Crown Court during the opening of the case against Adoboli.

"He was putting the very existence of the bank at risk."

(Reporting by Estelle Shirbon and Michael Holden; Editing by Maria Golovnina)