China's leader is expected to put the seal later on its contribution to what will be the first UK nuclear power plant to be built in a generation.
The plant could be opened by 2025 at Hinkley Point, in Somerset, with China likely to cover about 30% of the cost.
President Xi Jinping is meeting Prime Minister David Cameron later, on the second day of his UK state visit.
More than £30bn worth of deals between the UK and China are expected to be struck during the four-day visit.
The plant will be built by French energy firm EDF, in conjunction with a consortium led by Chinese state-owned nuclear company CGN.
Two other nuclear power stations, at Sizewell in Suffolk, and Bradwell in Essex, could follow as part of the deal with China.
Last month, Chancellor George Osborne visited China and secured the deal under which Beijing will invest in Hinkley Point.
Kamal Ahmed, BBC business editor, said: "In brute pounds and pence, it will be the largest inward investment ever in the UK.
"Such is the significance of the agreement, it will be left to the leaders of Britain and China to announce the partnership."
The Hinkley Point project has come under fire over its cost and the delays to investment decisions and the timetable for building.
The original plan was for Hinkley Point to start generating electricity by 2023.
The government has also been criticised for guaranteeing a price of £92.50 per unit of electricity - more than twice the current cost - for the electricity Hinkley produces.
That could mean higher bills for consumers, critics such as Greenpeace say.
The government insists that 25,000 jobs will be created and enough energy to power six million homes.
But opponents have also raised security concerns about allowing China a central role in Britain's nuclear future.
Meanwhile, from January, the government is planning to run a pilot scheme that will allow Chinese tourists to get a two-year tourist visa for £85 - these currently cost £324.
The prime minister's spokeswoman said the move was designed to boost the number of Chinese tourists coming to Britain.
The number has more than doubled over five years, with the tourism worth nearly £500m per year to the economy.