Havas, the French advertising agency, tipped as a takeover target after failing to acquire Grey Global, the US advertising firm, is to launch a €400m ($486m) rights isue and is considering putting a corporate raider on its board.

Vincent Bolloré, the businessman who made a €290m ($327m) profit on his Lazard stake four years ago, is seeking boardroom places after more than doubling his Havas stake to 10.4%.