Bank Sarasin said a former employee of the IT department who is accused of breaching client confidentiality by passing the bank account details of Swiss National Bank Chairman Philipp Hildebrand on to others acted alone.

Swiss National Bank Chairman Philipp Hildebrand pledged on Thursday to fight accusations of wrongdoing over the controversial trade by his wife Kashya and refused to step down.

She spent 400,000 Swiss francs (271,173 pounds) to buy dollars last August, just three weeks before the Swiss National Bank (SNB) imposed a cap on the soaring Swiss currency.

Instead of reporting transactions that he subjectively thought conspicuous to his line manager or to the bank's compliance department, the employee, according to his own testimony, confided in a lawyer who was known to him personally, Sarasin said in a statement on Friday.

The bank also said that Hildebrand had never been in contact with the IT employee and that Hildebrand had never put any pressure on his client advisor.

(Reporting by Catherine Bosley)