“Big Carl” lifted the 14-metre-tall dome to close the 44-metre-high reactor building, allowing its fit-out to accelerate.

The second unit is taking up to 30% less time to build thanks to the lessons learned from construction of the first phase.

On Unit 2’s civil construction, 30% fewer people achieved 40% more work than on Unit 1 with prefabrication of structures now approaching 60%

Stuart Crooks, CEO of Hinkley Point C, said: “The second of our two identical units shows the big benefits of repeating an identical design.

“Build and Repeat is the best way to build new nuclear with time savings already at 20-30%. All  our experience and innovation will benefit Sizewell C from the start.”