Grid operator warns again over power supplies in heatwave

Britain’s National Energy System Operator has issued a second warning in a week over electricity supplies as extreme heat squeezes the UK power system.

The operator asked generators on Thursday to provide any extra electricity they could for Friday evening, after a first margin notice earlier in the week and a costly round of balancing action to shore up supplies.

Neso said forecasts showed tight margins because of very high temperatures across Great Britain and the continent, but stressed that the electricity supply was not at risk and that the notice did not mean a blackout was imminent.

A week of interventions

The latest notice follows an earlier summer margin warning on Tuesday, June 23, which was later cancelled after extra supply was secured.

On Wednesday, June 24, Neso was reported to have spent about £10 million to secure extra power, including imported electricity and gas-fired generation, to avoid a supply crunch.

The second notice on Thursday, June 25, shows how quickly the system can tighten when demand rises and output from wind, gas and nuclear stations is all under pressure at once.

Why margins tightened

The heatwave is pushing up evening demand as households use air conditioners and electric fans. At the same time, low wind output has reduced renewable generation.

Thermal plants have also been affected. In Britain, heat has disrupted some gas-fired generation, while in France four nuclear reactors were reported to have shut down or reduced output because overheated river water limited cooling.

France is an important source of electricity imports into Britain, so weaker French nuclear output can add to regional tightness when UK margins are already narrow.

What it means for consumers

A margin notice is a routine balancing tool rather than a signal of immediate blackout risk, but repeated warnings can feed through to higher system costs.

Those costs matter because they can eventually be passed through into household and business energy bills, even when the grid remains stable.

The wider European heatwave has also lifted power-market pressure beyond Britain, with reduced generation and cooling constraints affecting multiple countries at once.

What to watch next

The key question is whether Neso will be able to lift the notice once additional supply is secured, or whether further intervention will be needed if the heat persists into the weekend.

Market attention will also stay on balancing-cost estimates from the first two notices, and on whether UK gas plants, French nuclear reactors or European imports remain constrained.

For now, the operator’s message is that supply remains available, but margins are thin and the system is being pushed harder than usual for late June.