Shares in Iberdrola, the Spanish energy giant that owns ScottishPower, rocketed more than 16% yesterday after European newspaper reports claimed France's EDF had built a stake of more than 3% and was poised to pounce in a takeover move.

However, as EDF denied it held Iberdrola shares, it became clear in the records from Spain's stock exchange regulator, dated January 22, that it was the French bank Natixis that had built a 3.9% stake in the Spanish utility.

Iberdrola shares yesterday climbed 16.7% to 9.09 (6.5p) on the Madrid bourse.

A spokesman for Iberdrola in Spain yesterday said: "We had no knowledge of EDF building a stake. However, once we heard the news, we immediately convened an internal takeover review committee, which comprises the company's most senior executives, as well as lawyers and other officials, to decide the best course of action to take in the best interests of shareholders.

"We are not against a takeover, as such, and the purpose of the committee is not to block any takeovers, but we were bound to take a look at this claim about EDF. And I repeat, we know nothing of it."

Asked if this internal committee was reconvened after it emerged that it was Natixis that had built a stake of more than 3%, obliging it to inform the Spanish market regulator, the spokesman said: "Absolutely not.

"Natixis is a traditional investor in Iberdrola, but we have no notion about what their motives might be in increasing the stake."

It remained unclear last night whether Natixis was holding its stake for a third party.

The Spanish power giant, which has its headquarters in Bilbao, in the Basque region, and operates in Spain, the UK, Latin America and the US, completed its £11.6bn acquisition of ScottishPower in April, 2007.

Meanwhile, a spokesman for Paris-based EDF yesterday added: "EDF expressed its interest in the Spanish market on several occasions, but EDF is not a shareholder in Iberdrola."