The latest setback will worry ministers in London who are trying to convince sceptics that nuclear can deliver quickly and efficiently to meet the looming energy "crunch" after 2015.
Jarmo Tanhua, chief executive of Teollisuuden Voima Oy (TVO), the Finnish electricity provider, said he was "extremely disappointed" that Areva had told it that the Olkiluoto 3 facility was not going to be completed until 2012 three years later than originally expected.
But he also attacked Areva and its German consortium partner Siemens for suggesting the embarrassing problems that have given valuable ammunition to the anti-nuclear lobby had been caused by the Finns.
"TVO is extremely disappointed that the consortium has not regardless of its responsibility as turnkey supplier and its earlier promises been able to complete the works on time or to mitigate its delays through effective acceleration measures," he said. "TVO totally rejects the consortium's accusations that TVO has any responsibility for the delay."
"The consortium incorrectly claims delays in document handling and approval, despite the fact that a large number of the documents it is required to prepare have still not been submitted for first inspection although the plant unit should almost be complete by now.
TVO has accepted for some time that the project was going to be blown off course but Areva said today that it could not be certain exactly when the station would be completed. Raising questions about whether the date could even be later than 2012, a spokesman said: "A major change in TVO's methods is required to set a definitive schedule for the project."
Industry figures with close contacts to Areva complained that the delays were being caused by the Finns taking 12 months to review vital safety documents rather than the three months that were agreed in the original contract.
This is one of a series of changes in the schedule that have shocked ministers and industrialists who want to see a new generation of atomic plants in Britain to meet an energy gap caused by old stations coming off line at a time when North Sea oil and gas is running out fast.
EDF, the French electricity provider that has been most vocal about its desire to build new plants in this country, has said it would like to have at least one facility working by 2017. EDF has been working closely with Areva, which has submitted for approval to the UK safety authorities a third generation of its European Pressurised Water Reactor (EPR).
Olkiluoto 3 is a 1,600-megawatt EPR and will be the first third-generation plant in the world. Work began on the project in 2005, when it was expected to take four years to complete. TVO announced in August 2007 that delays in construction had likely pushed the completion date into 2011. In December 2007 the company said that construction of the reactor would not be completed until summer 2011 and in October last year it predicted commissioning would not begin till 2012.