Ageing electricity cables leaking millions of litres of oil into ground

British energy firms' electricity cables have leaked millions of litres of insulating oil into the ground, the Guardian can reveal.

- Jasmine Owens

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

Oil serves as an insulating fluid inside older electricity cables, helping to keep them cool. But as they age, the cables start to leak.

The cables, mainly installed from the 1950s to the 1970s, pose a "huge problem for the environment", according to one scientist, while Greenpeace has described the issue as "really 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. It said many cables had been replaced, and oil-filled cables made up less than 1% of the grid around London and the south-east of England.