Aegis shares rose by 19% to 59p on the news yesterday, broken first by Brand Republic, and were up by 6.36% to 62.75p at 9.21am today.
Vincent Bollore, the biggest shareholder at Aegis with 29.9% and chairman of Havas, has doggedly pursued Aegis over several years, but has been constantly thwarted by the marketing group's shareholders, who have voted down five attempts by Bollore to secure board representation.
Speculation in the city that Lerwill's departure will trigger a renewal of Bollore's long campaign to take control of Aegis was also fuelled by the wording of a press release sent out by Aegis yesterday afternoon.
In the statement, John Napier, Aegis' chairman and the interim chief executive, made more than one reference to the two distinct companies that comprise the bulk of the company's revenues -- Synovate, a market research group, and Aegis Media, its network of media buying agencies, prompting speculation that the group could be broken up.
Synovate had been a target for Sir Martin Sorrell's WPP, which this year moved its attention to Taylor Nelson Sofres (TNS), and wrapped up a £1.1bn deal in October.
In 2004 he worked with Bollore on a bid that would have seen WPP take control of the market research business while Bollore took Aegis, which includes digital network Isobar.
The market research group could become a takeover target for the groups that missed out in WPP's successful pursuit of TNS.
It has been an eventful year for Aegis at boardroom level. In May, Mainardo de Nardis, the global chief executive of Aegis Media, left the company, replaced by Jerry Buhlman.
Last month, Aegis reported organic growth of 7.3% in the first nine months of the year, but warned of "slowing demand" in the UK, US and Spain. This month, Aegis Media lost the £650m Renault account to OMD, owned by rival Omnicom.
Insiders said Lerwill left after boardroom clashes with Napier, while the company's decision not to immediately replace Lerwill is seen as another sign the group may soften its stance to a takeover approach from Havas.
This article was first published on brandrepublic.com