The Spanish prime minister has reinforced his determination to block the sale of the country's energy firms to foreign buyers in an interview with a British newspaper.

Jose Luis Rodriguez Zapatero told The Times that he would not allow electricity firm Endesa to be sold to E.ON, the German heavyweight which has lodged an E26 billion takeover offer.

The Spanish authorities have instead backed a rival offer from Barcelona-based gas company Gas Natural, which is intended to create a national energy champion. However the European Commission has already stated its opposition to such a deal, arguing that Spain is acting in a protectionist manner to the detriment of the free market.

We support foreign investment, Mr Zapatero told the newspaper. In recent times, we have seen the arrival of important international companies – French, American. We only have one dispute regarding the energy sector, which we are very concerned about as a country.

He added that this was because Spain is heavily dependent on north African energy imports and unreliable hydroelectric infrastructure, and because it is one of only two major European countries without a state-controlled energy player (the UK being the other).

Meanwhile, Dow Jones Newswires reports that analysts it has spoken to believe E.ON will get the go-ahead to buy Endesa from the Spanish energy regulator, and that any conditions attached will not be enough to break the deal. However reports elsewhere suggest that the Comision Nacional de Energia will impose divestments so severe – including much of Endesa’s domestic generation portfolio – that E.ON will be forced to walk away.