If Mr Levy buys Aegis, he will create the world's largest media buying group, overtaking WPP. But Sir Martin doesn't want to let this happen - he and Mr Levy are old adversaries - so he has teamed up with a US private equity group, Hellman & Friedman, for a possible counter-bid. The intentions of Mr Bolloré - who felt moved to assure Havas shareholders at the annual meeting in June that he was "not the wolf, nor Darth Vader, so don't worry" - are less clear. He bought more Aegis shares last week, taking his stake up to 12.64 per cent, but has insisted it is a "purely financial investment". He has also been talking to Mr Levy, which adds to the intrigue.
So if Aegis is really up for sale, who is going to buy it? More to the point, is still more consolidation in the industry good news for advertisers? Agencies are now so big that some even dictate what kind of products their clients launch.
There is no doubt that Aegis is for sale - at the right price. It has not been screaming blue murder over these takeover approaches, and appears to be doing everything it can to engineer an auction. When Aegis announced it had received an approach from an unnamed suitor last month for around 140p a share, Publicis followed up the next day with an abrupt statement to the stock exchange. It confirmed that it had held "preliminary conversations" with Aegis but cautioned that it would be "premature" to assume that this would lead to an offer being made. Analysts say Publicis was bounced into responding by Aegis, whose own announcement was designed to bring other suitors - Sir Martin, for example - into play.
Mr Levy's interest is not in doubt. Anthony de Larrinaga from SG Securities says: "WPP has been flexing its muscles after buying Grey Global last year. It has been offering potential clients discounts, and promoting its bigger network compared with those of its rivals. Publicis needs to keep up."
Mr de Larrinaga is more sceptical about WPP's motives. For competition reasons, it can target only Aegis's market research arm, Synovate, which it could arrange to buy from Hellman & Friedman if a bid from the US venture capitalists were successful. "But there is an element of WPP wanting to thwart Publicis. WPP's involvement could also be a way of driving the price up," he adds.
That leaves Mr Bolloré who, as chairman and the largest shareholder of Havas, is keen not to see his fellow countrymen at Publicis scoop the prize. His stake in Aegis is not large enough to block a Publicis takeover, but analysts say he is in a win-win situation. Even if Publicis succeeds, he will make a quick profit on his investment.
Phil Georgiadis, the chief executive of media buying agency Walker Media, says the purchase of Aegis would sound the death knell for the global independent media buying agency. In the Seventies and Eighties, buying agencies split off from the creative agencies, which "looked down on them as barrow boys, even though they were astute businessmen", he says. These buying firms emerged as a threat to the big, established agencies by offering clients a better service.
"The big agency groups responded by trying to put the independents back into their box," explains Mr Georgiadis, whose company is majority owned by M&C Saatchi. Aegis would be the last major independent media buying agency to be repacked.
Some argue that mega-media groups are providing the best-value service to their clients, the advertisers. Giants such as WPP say they are a "one-stop shop", offering services including market research, pre-product launch advice, strategic planning, media buying, creative services and more. Bigger is better, they argue, because they can offer clients bundled services for less.
But with greater size and market share comes power. Not only are media giants in a stronger position to dictate terms; they can do the same for their smaller clients. Rather than allocate specific advertising space, big groups buy chunks of space through "agency deals", which are then parcelled out, some at discounts, some at premiums.
"Advertisers are beginning to ask questions about agency deals and worry about the transparency of the relationship between the media owner and the buyer," Mr Georgiadis says.
Chris Ingram, the chief executive and founder of the media consultancy Ingram and the communications group Tempus, argues that the mega agencies are responding to advertisers such as Coca-Cola which want their media bought on a worldwide basis: "Global advertisers feel thay need global companies to service them. This is driving consolidation, which is almost complete, but small advertisers lose out."
Growing bigger creates problems even for global groups because it creates conflicts of interest. For example, the consumer goods giant Procter & Gamble has bought Gillette but last week it had to switch Gillette's media buying contract from WPP's MindShare agency to local agencies, a move that worked to the benefit of Publicis. This was because MindShare already handles the media buying of Unilever, Procter & Gamble's bitter rival.
Graham Brown, the managing director of EMM International, which helps companies audit their advertising spend, says many advertisers are not seeing the benefits of consolidation. "Clients are almost bystanders in all this: they get less choice and are less powerful compared with these huge agencies."
Commercial broadcasters and other media owners declined to comment for this article, since the vast majority of the media-buying industry is owned by either WPP, Publicis or Havas. Smaller advertisers are similarly loath to speak out against these titans. But the media regulator Ofcom has responded to confidential complaints, and will be reviewing the relationship between commercial broadcasters and media agencies early next year. Clearly, some advertisers out there are not happy; their complaints will grow louder once Aegis is sold, so watch this advertising space.
FIRST AMONG EQUALS: THE DEAL MAKER, THE SEDUCER AND THE BUCCANEER
Sir Martin Sorrell
* Chief executive and founder of the WPP Group. Its companies include advertising agencies Ogilvy & Mather, J Walter Thompson, Young & Rubicam and the media consultancy MindShare.
* Makes no secret of his fondness for doing deals, which is just as well, as he has done literally hundreds of them, transforming the company from a wire-basket manufacturer to the world's largest communications group in less than 20 years.
* Famously predicted a "bath-shaped" prolonged advertising recession after the dot-com bubble burst.
* Admits he does not like to come second ("Maybe it's something to do with my size," the 5ft 6in Blackberry addict recently joked to The Independent on Sunday). As an example of his persistence (some may say obsession), it was reported that to help win the $400m (£275m) Samsung advertising account last year, he flew out to Seoul for a day to attend the opening of a museum sponsored by the family behind the electronics company. WPP won the account.
* Has a good track record bidding against the French. Beat off bids from Havas in 2001 for Tempus, the media buyer, and last year for Grey Global. Also saw off Publicis's 2003 bid for Cordiant.
* Chief executive of the French agency Publicis, the world's fourth-largest communications group. Its companies include media buying agencies ZenithOptimedia and Starcom MediaVest, and creative advertising agency Saatchi & Saatchi.
* Smooth-talking, immaculately coiffeured Frenchman, who joined Publicis in 1975 as an IT manager and was promoted to managing director within four years.
* Critics have accused him of arrogance. When Publicis lost out to WPP in the takeover battle for Cordiant two years ago, Mr Levy did not meet English investors in the company, unlike Sir Martin. This did not impress some of his advisers.
* Recently told the IoS: "I think that the role of advertising is to seduce. When you are seducing a person, you are not showing the worst part of your personality. You start by showing your smile." It remains to be seem whether Aegis's chief executive, Robert Lerwill, will be swept off his feet by Mr Levy.
* Recently installed chairman of the French media group Havas. Labelled the "Breton Buccaneer" by French brokers, but has come a long way.
* Started out by buying his family's struggling paper business (reportedly for one franc). First foray into media came in 1997 when he bought a stake in Bouygues, which controlled France's main commercial television channel TF1. Made a cool €200m (£140m) profit when he sold it a year later. Has repeated this smash-and-grab strategy many times, which has not endeared him to notoriously conservative corporate France.
* Turned his attentions to Havas last year, and has become its biggest shareholder with 22 per cent. Has also been building up a stake in Aegis, and now owns just under 13 per cent.