A nuclear reactor being built in Finland to the same design expected to be used in Britain is running three years behind schedule.

Its developers, Areva, the French nuclear energy group, and Siemens, of Germany, had hoped it would start generating electricity yesterday.

The reactor, in Olkiluoto, western Finland, is set to be the world's most powerful nuclear reactor, with a generating capacity of 1,600 megawatts — enough to power a city of 1.6 million people, or nearly one third of Finland's 5.5 million population. However, it is running three years late and is vastly over budget, beset by design delays, water-logged concrete and faulty pipes. EDF, the French state-owned energy group, has said that it will build at least four of the so-called EPR reactors — a new design — in the UK. The first, expected to be at Hinkley Point in Somerset, is slated to enter service in 2017 to help to plug a looming gap in Britain's energy supplies.

More than 4,100 people from 60 countries are working 24 hours a day to complete the Finnish plant, which has been designed to withstand a direct hit from a commercial airliner.

TVO, the Finnish electricity company, is paying a fixed price of €3 billion (£2.7 billion) for the new plant - even though costs have soared far higher than this.

“It's an enormous job,” Jounen Silvennoinen, project manager for TVO, admitted.

Supporters of the nuclear industry say that teething problems at Olkiluoto should be taken in context and were inevitable with such a landmark project. A second EPR is being built in Normandy, France, and is on time, although it, too, has exceeded its original budget. A further two reactors are slated for construction in China before construction begins on the first UK plant.

“It's very unfortunate that the project is delayed but safety and quality is our number one priority,” Kathe Sarparanta, communications manager for the project, said.

Olkiluoto 3 is the first nuclear plant ordered in Western Europe since the Chernobyl disaster of 1986.

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