Market research firm Taylor Nelson Sofres (TNS) is really playing hard ball with Sir Martin Sorrell’s WPP. It has now rejected yet another bid - an improved offer that, at £1.08 billion, valued it 52 percent more than last night’s closing valuation. But TNS said this still “substantially undervalues” it. Since it already opened its books to the ad giant last week, that must be code for: “We’ll need more than that, Martin.” Chair Donald Brydon said Sorrell is trying to “frustrate the GfK-Taylor Nelson merger for the benefit of WPP’s underperforming Kantar division” (via Marketwatch).

The Takeover Panel, which regulates mergers, has now given the two a deadline (pdf) of 7.30 next Wednesday, July 9, to seal the deal or drop the mating dance