Boris Johnson has greenlit funding for Sizewell C – the new multibillion-pound nuclear power station on the Suffolk coast.

Whitehall sources confirmed the Prime Minister and Chancellor Nadhim Zahawi have given the go-ahead for financing for the construction of the Sizewell C nuclear reactor in Suffolk.

Private funding will be sought for the project estimated to cost £20-30 billion.

The Government is then set to make a final decision on public investment early next year, with it expected to buy a 20% stake in the plant, costing up to £6 billion.

But Mr Johnson's decision to give the funding method the go-ahead in his last days as prime minister has come in for some criticism.

In a letter leaked to the Sunday Times, Chief Secretary to the Treasury Simon Clarke suggested that acting now would tie the hands of their successors.

Mr Clarke said the costs of Sizewell C are “sufficient to materially affect spending and fiscal choices for an incoming government, especially in the context of wider pressures on the public finances”.

While essentially a caretaker Prime Minister after being forced to resign over a succession of scandals, Mr Johnson previously said he would not be making major decisions before leaving office.

Alison Downes, a spokeswoman for Stop Sizewell C, said: "Whatever way you look at it, this is a very dodgy decision. Has it been made by a lame duck PM who is not supposed to tie the hands of his successor, or was it in fact made before Sizewell C was granted planning consent, lending serious weight to our conviction that this was a prejudiced, political decision?

"Our next Prime Minister should call Sizewell C in: there are so many better ways to spend billions of pounds of taxpayers' money than on a project that won't light a single lightbulb for at least a decade."

A Government spokeswoman said: “Nuclear power has a key role to play as we work to reduce our reliance on fossil fuels and exposure to volatile global gas prices.

“Negotiations are still ongoing on Sizewell C and as these are active and commercially sensitive discussions we cannot comment further.”

EDF has been contacted for comment.