EDF has announced a further delay to its flagship nuclear reactor project in France as it prepares to install the same design at power plants in Britain.

The company said that fuel loading at its Flamanville 3 project in western France will be done six months later than previously planned, adding €300m (£250m) to the project’s cost, which now stands at €12.7bn. 

A spokesman downplayed the likelihood of similar problems at EDF’s British sites, Hinkley Point C and Sizewell C, which will both use the same new EPR reactor design.

EDF, which is majority owned by the French state, owns nuclear power stations across the UK and France, and is planning expensive upgrades to its French fleet.  

The only site where its new EPR design is currently in operation is its co-owned Taishan nuclear plant in China, where one of its two reactors has been shut for repairs since June because of cracked fuel rods. 

Officials from the business and energy department said they were monitoring the situation closely and “did not want to pre-judge the outcome of various investigations”. 

Inspections at Taishan revealed “mechanical wear of certain assembly components”, EDF said. It added that several of its long-running reactors have shown a similar pattern and the issues did not raise questions over the Taishan reactor’s design.

EDF said that fuel will now be loaded at Flamanville in the second quarter of 2023. It blamed the delays on Covid disruption and added that steps to be taken before the fuel is loaded include learning lessons from Taishan.

A second EPR plant, Olkiluoto in Finland, is due to start up this month following long delays.

S&P Global Platts believes full operations will start at Flamanville 3 in January 2024. Construction began in 2007 but has been repeatedly pushed back, with lengthy repairs needed to its welding.

The latest delay comes as outages or closures across European nuclear power plants have added to pressure on power supplies, coinciding with a global natural gas shortage and helping to push energy costs to record levels.

Nuclear power accounts for about 20pc of UK annual power but most of its ageing nuclear fleet is set to shut down within the decade, with Hinkley Point C in Somerset and Sizewell C  in Suffolk the only new plants currently on the table.