After successfully reducing their debt mountains, Europe's biggest utilities are considering audacious deals and unexpected choices for advisers.

Last week's €22.7bn ($28.4bn) unsolicited bid by Spain's Gas Natural for Endesa, a local rival almost twice its size, is Europe's biggest announced mergers and acquisitions deal this year and heralds a return to big-ticket dealmaking by utilities. E.On, Europe's biggest utilities company, is also considering a €16bn all-cash offer for Scottish Power, a UK utility.