The government is to plough another £170million of taxpayers’ cash into the proposed Sizewell C nuclear plant.

The Department for Energy Security and Net Zero said the cash was in addition to the £679 million the government invested in the Suffolk power station late last year, when it took joint control of the project with EDF, of France.

Last year’s investment included about £100 million to buy China General Nuclear out of its 20 per cent stake. EDF said: “This is another big endorsement and will put us in an even stronger position to begin full construction.”

The government said the money would be used “to prepare the Sizewell C site for future construction, procure key components from the project’s supply chain and expand its workforce”. It said it was “previously allocated funding for development work”. The government pledged in the budget in 2021 to provide up to £1.7 billion “to enable a final investment decision in a large-scale nuclear project this parliament”.

Sizewell C could produce enough low-carbon electricity to power about six million homes. It is a proposed sister station to Hinkley Point C, under construction in Somerset, where work has been delayed and costs are estimated to have soared to as much as £33 billion.

The government and EDF have equal joint control of the development vehicle while they try to win investors to back the project, at which point their stakes are set to reduce to 20 per cent each. EDF has not provided an estimate for several years, but it is thought the costs could be as much as £30 billion.

Stop Sizewell C, a campaign group, said: “It sticks in the throat to see ministers splashing more taxpayers’ cash months before a final investment decision, while maintaining total secrecy about whether Sizewell C can achieve value for money.”