UBS chief Oswald Gruebel said in a memo that quarterly results issued earlier this week showed that the bank had made good progress despite a quarterly net loss, but warned that recovery will take more than just a few months, media reports said.

The firm posted a higher-than-expected third-quarter net loss and large client withdrawals at its core wealth management division, triggering a fall in shares. But UBS’s operating profit improved, once one-off charges were taken out of the figures. Results at the US, international and Swiss wealth management divisions were mixed.

"We have made good progress until now, which makes me optimistic. I am confident we will continue to move forward," Mr Gruebel was said to have remarked in the memo to staff.

The Swiss bank has suffered some of the heaviest losses in the credit crunch, booking more than $50 billion of write-downs it made on investments linked to the US mortgage market. It has also ceased to provide offshore banking in the US, after UBS became embroiled in a legal case over how a former employee helped US citizens evade taxes. And yesterday, the UK financial regulator, the Financial Services Authority, fined UBS £8 million for unauthorised trades at its wealth management unit.

"We do not want to shine in the short term by producing a few good numbers. Rather, we are working to create a new and sustainably profitable UBS, a firm that will never again make the same mistakes it did in recent years," Mr Gruebel’s memo said.

"That cannot be achieved in a few months. It takes more time because a lot needs to be changed,” he added.