Police have begun an investigation after protesters broke into one of Britain’s biggest power stations last week and cut almost 2 per cent of the country’s electricity supplies.

Up to 500 megawatts of generating capacity was lost from the national network for about four hours after the incident at Kingsnorth coal and oil-fired power station in Kent, The Times has learnt. An intruder scaled an electric fence, entered a secure area and switched off one of four turbines supplying London and the South East.

E.ON, the German power group that operates the plant, is understood to suspect that some of its own staff or contracted employees were involved in the incident last Friday night.

According to figures from National Grid, total UK electricity demand at the time was about 33,000 megawatts – meaning that 500 megawatts represented more than 1.5 per cent of the total, enough to power a city the size of Bristol.

The protesters, who have not been caught despite much of the episode being caught on CCTV, climbed an electric security fence that was not working at the time. Having switched off Unit Two, they left through an entrance that only employees would have been familiar with. They also managed to go through a complex procedure at a control panel inside one of the turbine halls to turn the machinery off.

Kent police are involved in the investigation. E.ON has ordered an internal investigation, and is examining its own security procedures.

E.ON has become a key target for climate change protesters because Kingsnorth has been earmarked for construction of Britain’s first new coal-fired power station in decades. The plant, which has a total generating capacity of 1,960 megawatts, making it one of Britain’s biggest power stations, is to be retired from service soon and E.ON wants to build a £2 billion coal replacement, which environmentalists say would lock in the emission of many millions of tonnes of greenhouse gases for decades to come.

Protest messages were also left strewn across the turbine hall during the incident.

An E.ON spokesman confirmed that an incident had taken place in which the site was entered illegally and equipment was tampered with. “While we are respectful of people’s right to peaceful and lawful protest, this was clearly neither of those and could have had very serious implications, not least because of the potential for serious injury or worse. Thankfully, our site team responded very quickly and professionally to ensure that the situation was brought under control.

“We have launched an investigation and are working closely with the police on their inquiries. Kingsnorth power station remains operational.”

E.ON has defended its plans for a coal-fired plant at Kingsnorth by saying that it would be fitted with equipment designed to strip out carbon dioxide for safe storage.

So-called carbon capture and storage (CCS) remains an experimental technology that has not yet been demonstrated on a commercial scale anywhere in the world.

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