Government funding for a new multibillion-pound nuclear power station in Suffolk is expected to be approved in the coming weeks.
Whitehall sources said it was unclear whether the government investment decision on Sizewell C would be made before the change in prime minister, but confirmed it was likely to be given the green light.
This funding relates to an initial pot of around £1.7bn, which is part of existing budgets.
A final investment decision is due to be made early next year by the new prime minister and could see the government put several more billions into the new plant.
Business Secretary Kwasi Kwarteng is understood to be pushing for the project, and Boris Johnson and Chancellor Nadhim Zahawi are also said to be on board.
Mr Kwarteng – who is tipped to become chancellor in a Liz Truss government – wrote in The Mail on Sunday that the government should “crack on with more nuclear power stations” in order to increase Britain’s energy security.
However other allies of Liz Truss appear to have expressed concern that making the decision in the next fortnight would bind the hands of the new administration.
In a letter leaked to The Sunday Times, Treasury Secretary Simon 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”.
Government sources said Mr Clarke was acting in his ministerial capacity as treasury secretary and the final decision on Sizewell C would be taken by the next administration.
While essentially a caretaker Prime Minister, Mr Johnson previously said he would not be making major decisions before leaving office.
Ms Truss, the frontrunner to replace Mr Johnson on 6 September, has pledged tax cuts, including a reversal of the national insurance hike costing at least £30bn per year.
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But she is under growing pressure to offer further support to the most vulnerable, as experts warn the energy price cap could exceed £6,000 in April in a further painful hike.
Development consent for Sizewell C was given the go-ahead in July, but negotiations over the financial investment decision were ongoing.
A government spokesperson 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.”