WPP, the British advertising giant, today launched a hostile bid for Taylor Nelson Sofres (TNS) but refused to raise its offer for the market research group above the £1 billion deal already on the table.

The company, led by chief executive, Sir Martin Sorrell, issued its offer this morning just ahead of a 7.30am "put up or shut up" deadline imposed by the City's Takeover Panel.

There had been expectations that WPP could increase its cash and share offer from 260p to 280p a share to tempt TNS shareholders to opt for its deal instead of the nil-premium merger the market research group is pursuing with Germany's GfK.

WPP today revealed it is sticking to its latest 260p a share offer that values TNS at just over £1 billion.

However, it may face increased competition from GfK which, as The Times revealed today, has joined forces with a financial bidder to potentially trump a bid from WPP.

Commenting on the deal, Sir Martin said this morning: "Reluctantly, we have waived our earlier pre-condition for the board of TNS to recommend our offer.

"Despite repeated efforts over more than three months to engage with TNS management, we have been unable to enter into any discussions that could lead to an agreement.

"Although our offer may be characterised by some as a 'hostile bid', we believe that it is in no way hostile to TNS share owners nor to TNS's clients and people. In fact, WPP believes it is more committed to maintaining the TNS brand than GfK."

He added that he believes WPP's offer is superior to "what is, in effect, a 'nil-premium' reverse takeover of TNS by GfK and a 'merger of unequals", and said the company remained willing "at the shortest of notice" to meet TNS's board.

Times Recommends

• House prices falling fastest in 18 years
• Britain 'faces full-year fall in GDP'
• Savills millionaire clients feel property crunch