Cedar Rock Capital, the largest shareholder in Taylor Nelson Sofres (TNS), has brushed aside a renewed attempt by WPP, the UK advertising giant, to acquire the market research group, branding it a "small increase on an offer that was way too low".

Andy Brown, chief executive and portfolio manager at Cedar Rock Capital, which hold nearly 10 per cent of TNS, spoke to Times Online after the market research group rejected a revised 241.5p per share. The new offer valued the company at £995 million, below last night's closing price of 246p.

Shareholders are waiting for TNS and GfK, the German market research group, to announce details of their nil premium merger, though investors said they were in no rush to receive the information.

Sir Martin Sorrell, chief executive at WPP, said yesterday that he believed that TNS's "proposed structure of the 'nil premium merger' with GfK is not conducive to maximising synergies."

He said: "We are again disappointed that our latest attempt to engage with TNS management on a friendly basis in order to deliver an attractive proposal for TNS shareholders has met with continued resistance...TNS's continuing refusal to share the same information which it has given to GfK (which is also a competitor) as part of their 'nil premium merger' discussions prevents us from operating on a level playing field."

Sources have indicated that investors are looking for at least 300p from WPP. It is understood that advisers to WPP have already had some contact with TNS shareholders.

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