The drawn-out Endesa takeover saga has entered yet another new chapter with German suitor E.ON accusing Spanish firm Acciona of launching an unlawful bid for its compatriot.

Having stayed the course long enough to see Spanish regulatory and law court hurdles overcome, E.ON now believes Iberian construction company Acciona is bidding to foil its plans to capture Endesa.

Just weeks ago, as E.ON appeared poised to secure its target Acciona increased its stake in Endesa by 13.69%, to lift it to a significant 19.63%. Now, according to reports, Acciona wants to further increase its share of the Spanish energy outfit to 35%.

In response, E.ON has accused the Spanish firm of launching an unlawful public takeover offer for Endesa and the German utility has extended its lawsuit against Acciona in the US courts in a bid to force the Spanish company to sell its recently acquired 13.69% stake.