GfK, the German market research group, has teamed up with a financial bidder in a last minute effort to prevent WPP from winning control of Taylor Nelson Sofres (TNS), The Times has learnt.

The German company, which is in talks with TNS about a nil-premium merger, plans to top any bid that WPP’s chief executive, Sir Martin Sorrell announces today.

If WPP offers a £1 billion plus cash and shares proposal of 280p per share, the GfK consortium may consider offering a 280p pure cash offer.

Should WPP announces its withdrawal, GfK is under no pressure to bid and the original plan for a nil-premium merger with TNS will take effect, subject to shareholder approval.

WPP, has a “put up or shut up” deadline of Wednesday to make a firm offer for TNS or walk away. Following a WPP board meeting tonight, the advertising giant is expected to announce its intentions as early as 7am tomorrow. The board of WPP has been discussing the group’s next move, but a pure cash offer is unlikely.

The advertising group gave an undertaking in an announcement earlier in the process that, if it made an offer for TNS, it would be structured to ensure that WPP’s credit rating would not be jeopardised. It is thought that the group believes a cash-only offer could impact its credit rating.

GfK has been keen to find an alternative solution if TNS shareholders accept a further proposal from WPP.

WPP’s last improved indicative bid of 260p per share, made up of 173p in cash and 0.1889 of a WPP share for each TNS share, valued TNS’s equity at £1.08 billion at WPP’s closing share price last Wednesday of 460.5p.

It is understood that WPP has been seriously considering going hostile and putting an offer directly to TNS shareholders.

However, some TNS shareholders have expressed concern about the shares element of WPP’s proposal, as WPP’s share price has fallen in recent weeks on concerns about the economic climate. WPP shares, which were 626p on May 2, closed yesterday at 464p.

One leading shareholder, who refused to be named, said last week that it wanted to see WPP table an offer closer to 300p, although it may consider one at about 280p.

There were mixed views about WPP’s last approach of 260p. Some analysts said that the WPP offer represented a fair price for shareholders and a premium of 52 per cent on TNS's share price of 171p.

Collins Stewart said in a note that the approach represented an “excellent deal for TNS shareholders”. Some hedge funds invested in TNS are thought to have shown support for WPP's offer.

WPP wants to merge TNS with Kantar, its own market research unit, to become the second-largest market research group after Nielsen. The combined group would have estimated combined revenues of $4 billion (£2 billion), doubling Kantar’s $1.9 billion figure for 2007.

TNS declined to comment.

Times Recommends

• Minister in talks with Saudis to protect creditors
• Premier Inn hits back in £29-a-room row
• Bankers hit back at 'populist' bonus supertax