Although WPP Group’s £1 billion ($1.9 billion) offer to acquire audience researcher Taylor Nelson Sofres was rejected over the the weekend, the UK ad holding firm is still pressing the TNS’ board for more talks, according to the Guardian. Sir Martin Sorrell, WPP’s CEO, made the bid for TNS shortly after the researcher announce plans to merge with German audience measurement company GfK. The deal with GfK is valued at £78.7 million (€100 million) and would create the second-largest audience measurement firm behind Nielsen.

TNS said it rejected WPP’s offer because it believed it was “not in shareholders’ interests” and undervalued the company. WPP has not said whether it will come back with a higher offer but a WPP spokesman said that the company has asked the board to provide more specifics on its decision, which Sorrell has characterized as “cavalier.” In turn, TNS shot back, through a spokesman: ”It doesn’t take long to reject a derisory offer.”

-- Reuters: Analysts seem to agree that WPP’s move is merely “opportunistic,” contending that the ad holding company was spurred to disrupt TNS’ merger with GfK, as a larger company with a blocking shareholder would ultimately make it more difficult to buy. They expect a higher bid.

• Audience Measurement Firm TNS Rejects WPP’s £1 Billion Offer