The facility is expected to cost at least £20bn and generate energy at a more expensive price when compared to renewables such as wind and solar.
The project is planned to commence before 2024, with construction taking between nine and 12 years, depending on developments at the oft-delayed and over-budget Hinkley Point C nuclear power station. French energy giant EDF recently pushed back Hinkley Point's first day of operation to September 2028.
The Department for Energy Security and Net Zero said the £170m funding for Sizewell C would be used to prepare the site for future construction, procure key components from the project's supply chain and expand its workforce.
The plant is being positioned as providing reliable, low-carbon baseload power to the UK energy grid, with a lifespan of roughly 60 years.
The funding announcement follows last week's launch of Great British Nuclear (GBN), a public body established to help deliver the UK's nuclear programme. It has a goal of providing 24GW of nuclear power by 2050.
According to energy secretary Grant Shapps, the body will help to boost the UK's energy security and reduce dependence on "volatile" fossil fuel imports. The nuclear industry is estimated to generate around £6bn for the UK economy.
"Sizewell C represents the bridge between the ongoing construction of Hinkley Point C and our longer-term ambition to provide up to a quarter of the UK's electricity from homegrown nuclear energy by 2050," he said.
"Our new nuclear fleet will provide clean, reliable and abundant energy while driving down bills, boosting economic growth and ensuring that the UK is never held to energy ransom by tyrants like Putin."
Like Somerset's Hinkley Point C, Sizewell C would comprise two reactors, generating a total of 3.2GW of electricity – equivalent to 7 per cent of the UK's electricity needs.
In November 2022, the government established a £700m investment scheme to fund Sizewell C's continuing development so it can reach the point of a final investment decision.
Nuclear and networks minister Andrew Bowie said: "The steps we're taking today will speed up the development of one of our biggest projects, Sizewell C, towards final approval, which would enable construction to start as soon as possible, supporting thousands of jobs for communities in Suffolk and across the country."
Following its creation last week, GBN launched a new competition for companies to secure funding support to develop products including small modular reactors (SMR).
Unlike conventional reactors that are built on-site, SMRs are smaller, can be made in factories and could transform how power stations are built by making construction faster and less expensive.
