Sir Martin Sorrell has waded into the conversation about the damning report from an industry body alleging media rebates and non-transparent practices are widespread in the US media buying landscape.

Business Insider is this morning reporting the head of WPP touched on the study from the National Advertisers Association at the company’s annual general meeting in London, believing the study was not independent, despite the ANA claiming it was.

“It is no way independent. It is one-sided. It does not include any input from any of the six major holding companies,” he is quoted as saying.

Of the six major holding companies – IPG, Dentsu Aegis, Omnicom, WPP, Publicis and Havas – the ANA report only references one.

Furthermore, the language used within the report had Sorrell saying it was “emotional and intemperate” and “deliberately stirs up the sort of question” about potentially dodgy practices in media buying.

Many others in the big agencies have also questioned the report’s validity, with Jerry Buhlmann, global CEO of the Dentsu Aegis Network claiming it was an “insubstantive report with subjective methodologies and anonymous input”.

GroupM, the media buying arm within WPP, released a global statement after the revelations, saying the report needed to be examined carefully.

“The ANA report and the objectivity of its authors and advisors needs to be examined carefully. The report should not be allowed to tarnish the entire industry, nor every company in it.  As we stated from the outset of the ANA’s exploration, GroupM does not seek, nor accept rebates or hidden revenues in any form from media partners in the U.S.; nor do we accept service fees from vendors that are not disclosed to clients.

“GroupM is straightforward with clients concerning our proprietary media products and the value they provide; clients always exercise an informed opt-in to participate. As we’ve already indicated, we insist that the ANA share any specifics relating to our group with us so that we can ensure continuing contract compliance.  If clients have any questions, they should contact us.

Locally, GroupM referenced its continual improvement to its systems and an introduction of guidelines for trading.

“GroupM are the most audited media group in Australia. Working with EY we have improved our systems and processes to even greater levels of compliance and quality assurance. We have the only dedicated compliance team in the country, which oversees a consistent national compliance process across all GroupM Australia agencies.