The Government is poised to give the green light to the controversial Hinkley Point nuclear power plant.
Downing Street and the new Department for Business and Energy are working flat out so that an agreement can be announced before the end of the week.
The Prime Minister wanted to announce on Monday that the project was back on but had to postpone the plans when the Cabinet minister in charge of the project said he had some last minute concerns.
She promised to make a decision by September.
A call was arranged between Mrs May and the French President François Hollande on Monday afternoon but it's understood the Business Secretary, Greg Clark - whose department is responsible for Hinkley Point - raised some questions at the eleventh hour.
It forced Downing Street to postpone the planned phone conversation with the Elysée Palace and it delayed the announcement that the project was back on track.
The whole process is a sensitive one as the plant is being financed by the French energy giant EDF and the Chinese General Nuclear Power Corporation.
Both Paris and Beijing are eager to reach a new deal with Theresa May's government - while she wants any new agreement on Hinkley to meet her fears over security.
It's thought the Prime Minister has insisted on a new contract which addresses her concerns that the UK is giving China a big stake in our nuclear power infrastructure.
The decision has implications for another nuclear reactor - Bradwell in Essex - which the Chinese want to build without French help.
Both sides are close to finalising the contract but new questions keep being raised which has delayed this week's announcement.