According to reports from Spain, the Madrid government has written a fierce letter to the European Commission, accusing it of exceeding its authority by threatening European court action over conditions attached to E.ON's purchase of Endesa.

Madrid’s El Pais newspaper carries details of the letter, which the commission says it will not respond to until it has had more time to examine its details. The Spanish government has apparently accused Brussels of approving E.ON’s E26 billion bid for Endesa with undue haste.

However the uncompromising EU competition commissioner Neelie Kroes sees the E.ON-Endesa deal as a touchstone issue that reflects how far member states are prepared to open up their energy markets.

The Spanish have been accused of protectionism after the Zapatero government openly favored a rival bid for Endesa from Barcelona-based Gas Natural. The government is also reportedly worried that the security of the Endesa’s power generating assets could be at risk if they are placed into German hands, as the Spanish feel security procedures employed by E.ON would not be as stringent as those of a domestic owner.

Observers feel that the 19 conditions imposed by the Spanish energy regulator on the E.ON deal, which include the divestment of almost a third of Endesa’s generating assets, were heavily influenced by the Madrid government.

The European Commission has refused to rule out taking the Spanish authorities to court over their attempts to derail the E.ON bid.