Société Générale has bolstered its defences against a potential bid, enlarging the roles of the banks underwriting a capital raising amid expectations of a bidding war for the French bank, which is understood to have already attracted interest from six European rivals.

The bank, which was struck by €4.9bn in losses following rogue trades, has now given JP Morgan and Morgan Stanley formal defence mandates on top of their roles as underwriters of a planned €5.5bn emergency rights issue.