Swiss bank Credit Suisse has reported its biggest quarterly loss since the collapse of Lehman Brothers six years ago as a result of the Sfr1.6bn (£1bn) fine from the US authorities for helping American citizens evade tax.

Brady Dougan, the bank’s boss, apologised for the Sfr370m in second-quarter losses caused by the fine, which he said “brought to a close the most significant and longstanding litigation issue for Credit Suisse”.

“I want to reiterate that we deeply regret the past misconduct that led to this settlement and we take full responsibility for it,” Dougan said.

The bank took the unusual step of pleading guilty to the charges when they were announced in May, which prompted calls for the resignation of Dougan, who has been at the helm of the bank throughout the financial crisis.

Despite outflows from western clients from its private banking arm, Credit Suisse still managed to attract Sfr10bn of new business.

After pleading not to shut down its commodities trading arm – as rivals such as Barclays are doing – Credit Suisse now intends to do so to free up capital to deploy in other areas of its business.