Ernst & Young's New York arm and one of its US partners are being sued over the alleged theft of trade secrets and confidential data from one of its client, Express Scripts.

In a complaint filed in a Missouri state court, pharmacy benefits company Express Scripts Holding claims that E&Y partner Don Gravlin had been 'sneaking' into its St Louis headquarters and emailing documents to a private Google account via the account of an E&Y consultant

The complaint alleges that this was done 'with an evil motive' to aid development of E&Y's own healthcare business unit, which includes Express Scripts, which it acquired last year, plus some of its competitors. The company alleges more than 20,000 pages of data were obtained in this way, including pricing information, business strategy, projections and performance metrics documents.

Express Scripts is claiming that E&Y and Gravlin violated Missouri computer-tampering and trade-secret protection laws, and is seeking damages plus a court order barring E&Y from the use or disclosure of any of the information it allegedly misappropriated.

A spokesman for E&Y in the US said: 'When we were notified about this matter several months ago, we immediately conducted an investigation and concluded there was a violation of EY policies and the company's policies. The individual at the centre of these allegations is no longer with the firm. We will vigorously contest the claims in the complaint.'