Head of marketing procurement Mark Coulson resigned prior to the investigation. Buyer Martin Simper remains in his position with the firm.

The investigation was launched after Vodafone was reported to be implementing a new print buying system developed by The Print Specialists, of which Coulson and Simper were previously directors.

A spokeswoman for Vodafone said the firm was continuing to review its print strategy while still operating in-house print buying.

Specialists was acquired by consultant Rob Sirett, whose firm I.See Direct conducted an audit into Vodafone's print procurement.

Coulson and Sirett were unavailable for comment.