MARKET research firm Taylor Nelson Sofres today fended off a third attempt by advertising and media giant WPP to muscle in on its planned £1.5bn merger with German rival GfK.

TNS told WPP and its chief executive Sir Martin Sorrell to “stop interfering” after snubbing the latest approach, which values TNS at £1.08bn.

TNS opened its books to WPP last month, but also criticised the firm’s “press commentary and innuendo” and accused Sir Martin of attempting to frustrate the merger with GfK,.

TNS chairman Donald Brydon said: “The board of TNS has been extraordinarily patient with Sir Martin Sorrell. We have now received three proposals from WPP, each of which substantially undervalues the company.”

And he added: “It is time for Sir Martin Sorrell and WPP to stop interfering and make their intentions clear.”