UK Gov's DESNZ Shows Nuclear Energy Hit Record Low in 2025

Britain's nuclear capacity has contracted over the past 10 years.

The loss could threaten progress on decarbonisation as gas generation compensates for the shortfall.

According to the Department for Energy Security and Net Zero, the country achieved 52.5% renewable electricity generation in 2025.

That figure represents the second year above 50%.

Nuclear decline fills with gas

The data also shows nuclear output dropped 12% to 35.9TWh last year.

That total is roughly half the volume produced in 2015. Gas generation increased 4.7% to 91.6TWh over the same period, claiming a 31.5% share of the grid.

Wind accounted for 30% of electricity generation. Total fossil fuel use rose 2%, with gas accounting for almost all of that increase.

The pattern suggests renewable growth alone cannot eliminate fossil fuel dependency without addressing baseload capacity.

The figures could reveal a tension in the energy transition. Renewable capacity continues to expand but wind and solar output fluctuates with weather conditions rather than demand patterns.

Nuclear provides consistent baseload power similar to gas. The UK fleet has lost that capacity as plants have closed and operational sites face unplanned outages. Several ageing reactors have experienced extended maintenance periods, reducing available capacity further.

Gas has filled the gap. That outcome reflects limited alternatives that can scale quickly rather than active policy preference for fossil fuels. The infrastructure already exists and gas plants can respond to demand changes within minutes.

The UK fleet has lost that capacity as plants have closed and operational sites face unplanned outages.

Several ageing reactors have experienced extended maintenance periods, reducing available capacity further.

Gas has filled the gap. That outcome reflects limited alternatives that can scale quickly rather than active policy preference for fossil fuels.

The infrastructure already exists and gas plants can respond to demand changes within minutes.

John Haw, Chief Executive at Fidelity Energy, frames the issue directly.

"The record renewable figures are genuinely impressive, but they're masking a problem," he says.

"Every time a nuclear plant goes offline for maintenance or decommissioning, gas turbines spin up to compensate.

"We're building a clean energy system on top of a baseload void, and until that void is filled – whether by new nuclear, grid-scale storage or something else – gas isn't going anywhere."

According to analysts, the final quarter of 2025 demonstrated the pattern. Nuclear output fell 13% in Q4 to 8.3TWh as outages continued across the ageing fleet.

The timing coincided with increased winter electricity demand, requiring greater gas generation to maintain grid stability.

Business exposure to volatility

The environmental consequences of increased gas use accompany financial effects.

Price volatility linked to gas markets continues to affect electricity costs. International events can trigger sudden price movements that ripple through business energy bills.

"What this means for businesses is that wholesale electricity prices remain far more gas-exposed than the renewable headline figures suggest," John explains.

"A company that thinks the grid is now 'mostly green' and therefore stable may be in for a rude awakening the next time gas prices spike," he adds.

Procurement strategies built on assumptions of steady decarbonisation may underestimate risk if they overlook the baseload gap.

Businesses could face unexpected cost increases when gas prices rise.

The sustainability credentials of grid electricity remain partially dependent on fossil fuel availability.

That dependency could persist until alternatives emerge.

Companies reporting carbon emissions based on grid averages may find their actual exposure to fossil fuels exceeds expectations during periods of low renewable output.

New nuclear faces delays

Most analysts and government officials agree additional nuclear capacity offers a solution. Hinkley Point C in Somerset is under construction but electricity generation is not expected until the late 2020s at the earliest.

The EDF-led project has experienced cost overruns and timeline extensions. Sara Stefanini, EMEA Climate Policy Editor at Carbon Pulse, has described it as a "headache" for around 10 years.

The Labour government has backed small modular reactors as a faster route to new nuclear capacity. GB Energy has struck deals with Rolls-Royce SMR for installations in North Wales.

That approach acknowledges the challenges of large-scale nuclear construction in the British context.

Traditional projects at sites like Hinkley and Sizewell continue but carry management risks.

Planning processes, regulatory approvals and construction timelines for conventional nuclear plants often extend beyond initial projections.

France generates around 70% of its electricity from nuclear power.

That fleet was built through decades of state investment and now provides some of Europe's lowest-carbon electricity at stable prices.

Whether small modular reactors can deliver at the required pace and scale remains uncertain.

The 2025 data suggests the transition has considerable distance to cover before baseload capacity matches renewable expansion.