On Tuesday the firm filed a counterclaim in a federal court in New York seeking to stop Kantar from selling its RapidView product. It follows a joint request last month from Kantar and WPP investment arm Cavendish for a district court to declare that Kantar had not infringed TRA’s patent.

In what is becoming a bitter dispute between two companies that have worked as close partners, TRA said yesterday it was shocked by the actions of its “supposed friend” in introducing a “directly competitive” service earlier this year, then launching litigation.

It said WPP had breached its duty of trust to TRA, stolen trade secrets, broken several agreements and infringed its patent relating to a process for “analysing return on investment of advertising campaigns by matching multiple data sources”.

TRA first unveiled its Media TRAnalytics service in 2008, around the time that Nielsen and Arbitron were winding up an ambitious joint venture, Project Apollo, which had sought to match purchase and viewing data by building a bespoke panel.

The firm claims to have access to set-top box data from two million US homes under partnerships with cable and TiVo subscribers, while Kantar’s rival service uses data from around 100,000 homes through a tie-up with satellite TV provider DirecTV. Both companies’ products rely on the same transaction data, which Kantar licenses to TRA for use in its service.

Mark Lieberman (pictured), TRA’s chairman and CEO, said: “WPP has been a trusted partner, investor, board member, licensee and vendor for over three years so we are shocked that they would launch a directly competing product that infringes our patent and then decide to resort to the courts for resolution. While copying is the sincerest form of flattery and certainly validates TRA’s solution, we will always protect our shareholders’ investment in our proprietary technology and patents.”

WPP and Kantar declined to comment on the matter today.