UBS stunned the markets on Thursday by revealing that a 31-year-old trader had been arrested in London on suspicion of blowing a $2bn hole in the bank’s books, three years to the day after Lehman Brothers collapsed.

Kweku Adoboli, a director on the Swiss group’s little-known “Delta One” derivatives desk, was being held at Bishopsgate police station after he was arrested at 3.30am, as the Swiss group’s shares plunged 10 per cent in response to the news.

UBS warned that the discovery – which drew parallels with the €4.9bn ($6.8bn) hit caused to Société Générale by Jér?me Kerviel in 2008 – could push the group into a loss for the third quarter. “We understand that you have already had to contend with unfavourable, volatile markets for some time now,” Oswald Grübel, UBS’s chief executive, said in a memo to employees. “While the news is distressing, it will not change the fundamental strength of our firm.”