Italian leader Bonelli Erede Pappalardo has won a major role advising Enel on its acquisition of a stake in Endesa, in a move that plunges it into the bidding war for the takeover of the Spanish utility giant.

Name partner Sergio Erede advised the Italian electricity group – a long-term client – on acquiring the shares.

Enel purchased a 9.9% stake in Endesa for A4.1bn (£2.8bn) at the end of last month (27 February) before taking a further 7% stake via a share swap deal with UBS last week (1 March). It is understood Enel wants to boost its holding to 24.99%.

The moves are significant as Enel's stake, combined with the 21% stake acquired by Spanish energy firm Acciona last year, could threaten E.ON's proposed A37bn (£24.9bn) takeover bid for Endesa, currently the largest M&A bid in Europe.

Spanish independent Uria Menendez is advising Acciona. Clifford Chance managing partner Ignacio Ojanguren is leading the team for Endesa.

E.ON has been involved in a bidding war for the Spanish utility company since February last year after it made a counter bid against Gas Natural's A22.5bn (£15.4bn) hostile offer. E.ON had been expected to have a clear run at the acquisition after Gas Natural dropped out of the bidding war last month (1 February).