Millions of litres of oil seeping into UK soil from ageing electricity cables | Pollution

Electricity companies are leaking millions of litres of oil underground throughout the UK, the Guardian can reveal.

In the past 15 years, 3m litres (660,000 gallons) of oil has been spilt under southern England from cables owned by the electricity distribution company UK Power Networks. But leaks are occurring UK-wide; the largest single leak reported in recent years was in Edinburgh, when 24,000 litres was spilt from a ScottishPower Energy Networks (SPEN) cable.

The oil is inside ageing electricity cables that were mainly installed in the 1950s to 1970s. It acts as an insulating fluid and helps to keep the cables cool, but as the cables age they leak increasingly.

One scientist who has researched the cables said the leaks presented a huge problem for the environment, while Greenpeace has described the findings as extremely concerning.

The Energy Networks Association (ENA), which represents the electricity distribution companies, said heavy oil had not been used in new cables for 40 years and many cables had been replaced. UK Power Networks said it had made investments to reduce leakage and was committed to replacing the cables entirely in the long term.

Dr Susmit Basu researched the underground cables between 2015 and 2018, when he worked at a science and technology company that conducted research and development for a UK Power Networks project focusing on reducing oil leaks from them.

He said the leaks presented a “huge problem for the environment” and were slowly contributing to major biodiversity loss over long periods of time.

Basu visited one site in Norfolk where a cable was leaking oil continuously and had saturated the soil. The oil had seeped into the bodies of trees via the roots, then damaged leaves and caused them to become yellowish in colour and develop spots. The oil-soaked soil had to be removed and replaced with fresh soil. But no one knew “how much of the fluid the rainwater took with it – that was anyone’s guess”, Basu said.

Usually an underground oil leak caused no immediate danger, Basu said; it was rarely the case that “this night there was a leak and tomorrow it was a disaster zone”. But with time the oil travelled through the soil into the nearest water bodies including rivers, lakes or the sea, killing useful fungi, bacteria, fish and other aquatic life.

Maintenance workers often topped up cables when a drop in oil levels caused them to stop working effectively, Basu said. “Where’s those few thousands of litres going?” He said the leaked oil would “not simply disappear” and would stay in the environment for thousands or millions of years.

Basu said companies were introducing solutions to the leaks, but doing so was costly and could be complicated.

He also suggested there was little public pressure to act: “The leaking is invisible to the public eye … nobody cares [about the leaks], nobody knows, nobody can see. Those materials should not be in the soil … we need electricity but we also need the environment and our surrounding atmosphere to be clean.”

Companies and regulators do not publish information about precisely where leaks have occurred or oil-filled cables are located, though freedom of information requests from environmental regulators reveal leaks have happened underneath cities, residential areas, riverbeds and arable fields.

Lily-Rose Ellis, a campaigner at Greenpeace UK, said: “This is really concerning and is yet more evidence of the urgent need to update our crumbling energy infrastructure. “These cables are at best outdated, but some are virtually antiques and are urgently in need of replacement. The UK electricity grid was designed and built for the energy system of the last century.”

UK Power Networks is responsible for more electricity cable leaks than any other company, freedom of information requests to the energy regulator, Ofgem, have confirmed.

Electricity North West, Northern Powergrid, Scottish and Southern Electricity Networks (SSEN), SPEN and National Grid Electricity Distribution (formerly Western Power Distribution) all also own fluid-filled cables.

The largest single spill recorded in recent years was underneath Edinburgh. A single SPEN cable leaked 24,000 litres of oil between late 2023 and its being sealed in early 2024. An additional ScottishPower cable leaked a further 6,000 litres in Edinburgh in 2023. The Scottish Environment Protection Agency refused freedom of information requests for details on the Edinburgh leaks on the grounds that an investigation was taking place. SPEN stated at the time: “Neither leak has resulted in oil contamination of watercourses, and no enforcement actions or undertakings resulted from the two incidents notified to the regulator.”

A spokesperson for ENA said the electricity distribution companies had not used heavy oil in newly laid fluid-filled cables for about 40 years and now used biodegradable substances, solid insulation and sealed cabling. It said 310 miles of older cables had been replaced in the past 10 years, and oil-filled cables made up less than 1% of the grid around London and the south-east.

UK Power Networks said it had made significant investments to reduce oil leakage since 2011, replacing 78 miles of oil-filled cables, and was committed to replacing them entirely. It said it worked with the Environment Agency for reporting and mitigation and adhered to relevant operating codes. It said: “During repairs, the company recovers as much cable fluid as possible.” This included fluid pumped into containers and oil absorbed in contaminated soil, which is removed in sealed skips and disposed of by specialists.

Ofgem said it had made it clear to companies that they should do everything possible to mitigate the impact on the environment, including preventing leaks by ensuring their assets were well maintained and reliable.