Chinese interest comes at a time when London is looking to replace ageing coal and nuclear plants set to shut in the 2020s but struggling to do so given the costs involved. If CGN's investment goes through, it will give the firm, China's largest nuclear power operator, stakes in four British nuclear plants.

"We are willing to utilize our experience in nuclear design, construction and operation for more than 30 years to support the development of Britain's nuclear industry," CGN said in a statement to Reuters on Tuesday.

It did not further elaborate on its proposed investment in NuGeneration (NuGen), which plans to build three nuclear reactors at the Moorside site on the coast of Cumbria, northwest England, in a project valued at $15 billion to $20 billion.

NuGen plans to build the reactors using technology from Toshiba's bankrupt U.S.-based nuclear arm Westinghouse. The technology is currently being assessed by Britain's nuclear regulator. The three reactors will have a total generating capacity of up to 3.8 gigawatts, covering around 7 percent of Britain's electricity demand.

NuGen was set up as a 60-40 percent joint venture (JV) between Toshiba and Engie. But earlier this year, the French utility sold its stake to Toshiba after Westinghouse filed for bankruptcy.

Toshiba said at the time it was looking for more investors to join the Moorside project or to sell out altogether.

British newspaper The Times on Monday first reported CGN's was exploring an investment in NuGen.

The Shenzhen-based group already has a 33.5 percent stake in Hinkley Point C nuclear power station project, Britain's first new nuclear plant to be built in decades.

It also owns 20 percent of a new power station at Sizewell in Eastern England, and will take a 66.5 percent share in a JV firm behind the nuclear power project at Bradwell-on-Sea in Essex, southeast England.

Apart from CGN, Korea Electric Power Corp (KEPCO)(015760.KS) has also shown an interest in acquiring a 60 percent stake in NuGen from Toshiba and had been negotiating informally, its CEO Cho Hwan-eik told local media in March.

(Reporting by Julie Zhu; Editing by Himani Sarkar)

By Julie Zhu