Swiss prosecutors have widened a probe over the leaking of private bank information that helped force the head of the Swiss National Bank to resign.

The home and firm of the former justice minister and rightwing Swiss People's Party strongman Christoph Blocher were searched on Tuesday as part of the criminal inquiry, according to a statement from the Zurich prosecutor’s office.

Blocher's spokesman Livio Zanolari declined to comment.

Former SNB head Philipp Hildebrand resigned in January after emails cast doubt on his claims not to have known about a lucrative foreign exchange trade made by his wife Kashya in August, weeks before the SNB moved to stop the Swiss franc climbing.

Hildebrand had been accused of insider trading after details of the currency transactions were leaked. The SNB chairman denied the charge, maintaining his wife ordered the transactions without his prior knowledge.

In January, prosecutors opened criminal proceedings against two members of Blocher's party, a lawyer and a Zurich cantonal parliamentarian, who are both accused of passing on data on Hildebrand's account in breach of the country's strict bank secrecy laws.

Blocher, a vocal critic of Hildebrand’s actions while chairman of the SNB, has already been questioned as part of that investigation. He denied handling any original banking documents in the matter and said that he merely relayed information to the cabinet.

An IT worker at Bank Sarasin had admitted passing the confidential information to the lawyer. The bank fired the employee and pressed criminal charges against him and unnamed third persons for violations of bank client confidentiality.

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