EDF Energy has warned that a flagship nuclear power station it is building in France could run further behind schedule and over budget, after it detected faults at the €10.5bn ( £9.2bn) plant.

The French state-owned firm said inspections last month had uncovered problems with welding on pipes at the Flamanville plant in north-west France.

Flamanville’s reactor design is the same as the one being used at a delayed plant in Finland and at Hinkley Point in Somerset, where EDF is building the UK’s first new nuclear power station in decades.

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The company said that it had discovered “quality deviations” on 150 welds in a system used to transport steam to turbines used for electricity generation.

EDF said it was performing further checks to see what works would be needed to satisfy the safety requirements of the French nuclear regulator, ASN, and would report back in May.

In a statement, the firm said: “Following the current checks and the licensing process by the ASN, EDF will be able to specify whether the project requires an adjustment to its timetable and its costs.”

The plant is already three times over its original estimates and several years late.

Nuclear industry experts said the announcement cast doubt over whether Flamanville unit three would be operational by the end of 2019, as planned.

Stephen Thomas, professor of energy policy at the University of Greenwich said: “If remedial work is needed, this puts in further doubt whether Flamanville can be in commercial operation [as previously planned].”

ASN warned earlier this year that the start-up schedule for Flamanville was tight.

Paul Dorfman, of the Energy Institute at University College London, said the problems did not bode well for Hinkley Point C, which is due to come online in 2025.

“If they can’t build their own reactor in France, where can they build it? This seems counter to their claims that they are learning from their mistakes and Hinkley won’t be a repeat.”