In its legal claim, filed in London’s High Court, Group M said that FirmDecisions had given a “wholly inadequate” assurance that it had deleted all trace of the “four or five” different, confidential documents, which are thought to include details of clients’ media spend.

Group M, WPP’s media-buying arm, claimed FirmDecisions may be “in breach” of its non-disclosure agreement between the two companies. The court filing also quoted a “senior FirmDecisions employee” as saying the media auditor planned to keep a document “up our sleeve” to use at a later date.

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