Boris Johnson has greenlit funding for a new multibillion-pound nuclear power station, triggering concerns among some of Liz Truss's allies that it could limit her economic vision.
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.
Business Secretary Kwasi Kwarteng, who is tipped to be Ms Truss's chancellor if she wins the Tory leadership race, is said to be "massively" on board with the plan.
But her camp did not appear to be united on the issue, with Chief Secretary to the Treasury Simon Clarke raising concerns with Mr Johnson and Mr Zahawi.
In a letter leaked to the Sunday Times, Mr Clarke suggested that acting now would tie the hands of their successors.
Mr Clarke, who is expected to get a senior Cabinet job if Ms Truss wins, 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.
Ms Truss, the frontrunner to replace Mr Johnson on September 6, has pledged tax cuts, including a reversal of the national insurance hike costing at least £30 billion per year.
But she is under growing pressure to offer further support to the most vulnerable, as experts warn the energy price cap could surpass £6,000 in April in a further painful hike.
Mr Kwarteng, in an article for the Mail On Sunday, promised "help is coming" but insisted it is "entirely reasonable not to detail the exact shape of that support" until later.
He also stressed the need to "crack on with more nuclear power stations" in order to increase Britain's energy security.
Development consent for Sizewell C was given the go-ahead by Mr Kwarteng in July, but negotiations over the financial investment decision were ongoing.
