Sizewell B extension to 2055 bolsters UK low-carbon power

The news

The UK Government has agreed a 20-year lifetime extension for Sizewell B nuclear power station. This will allow the plant to continue operating until 2055 instead of its original planned closure in 2035. Sizewell B currently generates about 3% of the UK's electricity and produces enough power for around 2.5 million homes, according to government announcements reported in July 2025.

What's at stake

Sizewell B is one of the UK’s largest low-carbon power sources. Its extension would maintain reliable baseload electricity equivalent to the needs of 2.5 million homes for two extra decades while the country pursues net-zero targets. The decision forms part of a broader push that includes approval for the One Earth Solar Farm, the second largest solar project in the UK to receive planning consent.

The extension also sits alongside wider nuclear ambitions. Industry analysis indicates more than £100bn of expected investment in the country’s civil and defence nuclear programmes over the next decade. This investment is framed as a once-in-a-generation opportunity to strengthen manufacturing, improve energy security and support long-term economic growth.

At the same time, the UK offshore wind sector faces its own transition. Approximately 5 GW of UK offshore wind capacity is expected to reach the end of its life in the early to mid-2030s, requiring decisions on repowering or decommissioning.

The case for

Extending Sizewell B delivers reliable low-carbon electricity and strengthens energy security for two more decades. The plant’s 3% share of UK electricity supply provides consistent output that renewables alone cannot yet match at scale, reducing reliance on imported fuels. Keeping the station running until 2055 avoids an immediate supply gap and supports the net-zero pathway outlined in government policy.

Comparable extensions have been used successfully in other countries to maintain low-carbon capacity while new projects come online. The move also preserves skilled jobs and supply-chain expertise that would otherwise be lost upon early closure.

The case against

Extending Sizewell B delays investment in newer nuclear and renewable technologies. Resources and policy attention focused on prolonging an existing station could instead accelerate deployment of advanced reactors and the next wave of offshore wind or solar projects. With £100bn of planned nuclear investment over the coming decade, prioritising modern facilities would better position UK manufacturing and supply chains for future growth.

Offshore wind decommissioning planning is already under way for 5 GW of capacity in the early to mid-2030s. Accelerating replacement with newer renewable and nuclear capacity would maintain momentum towards a more diverse and flexible low-carbon system rather than relying on extended operation of older infrastructure.

Why it matters now

If the extension proceeds, Sizewell B will continue supplying 3% of UK electricity until 2055, providing a stable bridge while new nuclear and renewable projects scale up. A decision to close in 2035 would require faster replacement capacity and could increase short-term pressure on energy security. The next major milestone will be progress on the £100bn nuclear investment pipeline and decisions on repowering or decommissioning the first wave of offshore wind assets in the early 2030s.

Further reading

edie.net · Financial Times

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