An after-hours raid by Acciona on Endesa’s shares this week means that Eon may have to learn to work with the Spanish construction and energy group if it wins the long-fought battle for Endesa.

Acciona burst into the arena on Monday night, snapping up 10 per cent of the company at €32 a share, triggering the German group’s revised, €35 bid on Tuesday night. By Wednesday night, the Spanish company had amassed another 5 per cent, in the form of share options that it will exercise if it gains approval from the national energy commission. Company executives say they want to build a 25 per stake and get involved in the management of Endesa.