Sir Martin Sorrell's WPP Group pulled out of a joint takeover approach for Aegis, after its indicative offer was rebuffed, leading the companies into a public squabble over how much any deal could have been worth.

The world's second-biggest advertising company said it had "no intention" of making another offer after seeing two separate all-cash offers rejected. One of the deals on the table involved a joint bid between WPP and Hellman & Freidman, while the other was a three-way approach in concert with a party it did not name.

Media buyer Aegis then released a statement saying it rejected the bid because the initial non-binding approach from WPP and Hellman & Friedman was "materially below" the 140p per share level offered by French ad house Publicis in September. Aegis said it was not asked to consider any proposal involving any other party.

"Today's announcement was not a surprise, given that WPP and Hellman & Friedman had not made a credible proposal to the board," said Robert Lerwill, chief executive of Aegis.

Sir Martin reposted by saying it was offering to pay 130p per Aegis share, potentially rising to "in excess of 140p" per share once ownership of the new company was fiinalised. WPP had earlier reserved the right to return to the table after French billionaire Vincent Bolloré was given the green light to make his own bid.

WPP last month teamed up with American finance house Hellman & Freidman to explore a takeover of Aegis, Europe's last major independent media buyer. At Aegis's request, the Takeover Panel set a "put up or shut up" deadline of noon today for the companies to announce their plans, or be barred from an offer for six months.

The regulator also said today that Mr Bolloré, Aegis's biggest shareholder, would not be bound by the restrictions that now apply to WPP and Hellman & Friedman. That leaves the French entrepreneur and chairman of French ad giant Havas free to make an offer for the whole company, should he choose to do so.

Mr Bolloré is understood to have held detailed discussions with WPP and Hellman & Friedman about making a concert offer for Aegis. Industry analysts believe WPP was most interested in Synovate, the company's market-research arm. Havas, meanwhile, would be attracted by Aegis's Carat agency, which would give it a market-leading 13 per cent share of the media buying market.

However, experts now believe Mr Bolloré is unlikely to make a full approach for Aegis, and instead will look to increase his stake to just below the 30 per cent limit that would trigger an automatic bid. He may then use the holding as leverage to gain seats on the company's board, using a similar strategy to the one he used to gain control of Havas after building a 22 per cent stake.

"We believe (Mr Bolloré ) will continue to pursue collaboration with Aegis and Havas. However it is hard to see how this would benefit Aegis shareholders near term." Alex DeGroote, an analyst at Panmure Gordon, said in an e-mail.

Analysts argued that Aegis is now most likely to stay independent, at least in the short term, as the list of potential buyers has dried up. Omnicom, the world's largest advertising group, was reported to have looked at Aegis last year but decided not to bid.

WPP shares rose 11.5p or 2 per cent to 577.5p by the close of trading on the London Stock Exchange, as shareholders described the possible purchase of Synovate as "far from a must-do deal". Aegis shares sank 3.25p or 2.7 per cent to 117.75p.

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