The state prosecutor of the canton of Zurich said on Thursday it was starting an investigation into a former employee of Bank Sarasin for having broken the law and made public bank data pertaining to the director of the Swiss National Bank.

The state prosecutor of the canton of Zurich said it was starting a criminal investigation of a 39-year-old man who had worked in the bank's IT department.

Switzerland's top central banker is facing intense pressure over a controversial currency trade made by his wife three weeks before he oversaw moves to impose a cap on the Swiss franc.

SNB Chairman Philipp Hildebrand will break his silence over the episode at 3 p.m. British time after the former employee of his family's bank leaked details of the trade to the lawyer of a political adversary.

(Reporting by Catherine Bosley)