Developer EDF revealed the latest in a series of setbacks for the budget and timeline after completing design for the fitout.

It said this had given it clearer sight of the final outturn cost and schedule.

The cost of completing Hinkley is now put at between £31bn and £34bn.  Although, if completion of the first reactor unit is delayed to 2031 in its worst-case scenario, costs would rise to £35bn at 2015 prices.

The second unit would be online about a year after the first, according to EDF.

In 2022, after assessing the impact of the pandemic, EDF said the targeted start of electricity generation was  June 2027, while final construction costs were estimated at between £25bn and £26bn.

At today’s prices, the actual cost balloons to £46bn.

Hinkley Point C’s managing director Stuart Crooks, said that running the project for longer and the rising cost for civil construction meant the power station would cost more.

“We’ve put the dome on two years later than planned in the schedule we started with. Around 15 months of that delay was due to the global pandemic.

“Restarting the British new nuclear industry has been hard,” he said.

“We’ve had to train a new workforce, teach suppliers to build nuclear and like any other developer, change our design to meet British regulations.”

This meant 7,000 design changes, 35% more steel and 25% more concrete.

Crooks added that like any other major infrastructure project Hinkley had also faced inflation, labour and materials shortages.

Looking forward, he said that big lessons had been learned on reactor one, with the second unit now being built 20-30% faster.

While the taxpayer will not foot the extra spend, the cost revision comes at a sensitive time for the government.

Under the funding plan for construction of Sizewell C, the Government has agreed to allow construction costs for a new plant in Suffolk to be added to customers’ bills gradually over the course of the build programme.

This differs from the model for Hinkley C where EDF agreed to shoulder the risk on the project in return for an agreed electricity sale price that was substantially higher than the average rate.