The owner of Hinkley Point C in Somerset has warned that the much-delayed construction of Britain’s first new nuclear power plant in a generation could face further hold-ups because of a row over its impact on local fish.

The nuclear developer, EDF Energy, warned that the “lengthy process” to agree to a solution with local communities to protect fish in the River Severn had “the potential to delay the operation of the power station”.

As a result, the developer, which is owned by the French state, raised the threat of further delays to Hinkley Point – a project already running years late and billions of pounds over budget.

EDF said last year that Hinkley could be delayed to as late as 2031 and cost up to £35bn, in 2015 money. The actual cost including inflation would be far higher. EDF declined to say how long any new delay could be.

The prospect of a fresh delay to the plant, which is expected to generate about 7% of the UK’s electricity in the 2030s, comes amid a deepening row between green groups and the government over the chancellor, Rachel Reeves’s plan to prioritise economic growth over other considerations, including the environment and net zero.

EDF last week welcomed the government’s new reforms to “stop blockers getting in the way” of new infrastructure projects, including nuclear power plants. It called for the government to establish a framework to manage environmental concerns “in a more proportionate” manner.

The developer has pressured the government to loosen environmental rules while at loggerheads with local communities over its complex plans to protect local fish populations which are at risk of being sucked up into the nuclear power plant’s cooling systems.

The company had planned to install an “acoustic fish deterrent” to keep fish away from the reactor’s water intake system, which is nearly two miles offshore.

The project, which was reportedly informally dubbed “the fish disco” among former ministers, would require almost 300 underwater speakers to boom noise louder than a jumbo jet 24 hours a day for 60 years.

But the plan was later scrapped by EDF over concerns for the safety of divers who would need to maintain the speakers in dangerous conditions. There are also questions over its effectiveness.

Without the deterrent an estimated 18 to 46 tonnes of fish could be killed every year, according to estimates provided by EDF.

The company dismayed local farmers and landowners last year by suggesting plans to turn 340 hectares (840 acres) of land along the River Severn into a salt marsh to compensate for the number of fish forecast to be killed by the reactor every year.

After a growing outcry, it said earlier this month it would delay the formal consultation on its salt marsh plan, which it says would provide safe habitats for fish and animals, from the end of this month until later this year.

Mark Lloyd, the chief executive of the Rivers Trust, said any fish deterrent was vital. “The water intakes will suck in an Olympic swimming pool’s worth of water every 12 seconds, more than the normal flow of all the rivers flowing into the Severn estuary, and without a deterrent mechanism will cause a vast slaughter of millions of fish every year for the next 60 years.

“This will cause the potential extinction of populations of rare and endangered species … As the Severn estuary is a vital fish nursery for the whole region, the strategic and economic impacts for marine fisheries throughout the Irish Sea will be devastating.”

The Hinkley Point project is seen as an important part of Britain’s plan to meet its legally binding target to reduce its carbon emissions to net zero by 2050. But it has already faced lengthy delays and spiralling costs.

In 2007, EDF had said turkeys would be cooked using electricity generated from Hinkley by Christmas 2017. When the project was finally given the green light in 2016, its completion date was set at June 2027 and the cost was estimated at £18bn.

The company has called on the government to set new planning reforms which ensure that the need for environmental safeguards are determined “in a proportionate and reasonable way”.

In a statement, EDF said: “Hinkley Point C is the first power station in the Severn to have fish protection measures in place, with a specially designed low-velocity cooling water intake system and a fish return system.

“However, the current lengthy process to identify and implement acceptable compensation for a small remaining assessed impact on fish has the potential to delay the operation of the power station.”

The cost of Hinkley’s sister project, at Sizewell C in Suffolk, has doubled to £40bn since plans were presented in 2020.