Britain’s electricity grid operator has issued an industry warning of a potential power supply squeeze on Wednesday evening, as extreme heat places significant pressure on the national system.
The National Energy System Operator (Neso), the body responsible for ensuring electricity supply meets demand, confirmed it had issued an "electricity margin notice".
This marks a rare summer intervention, as the country braces for what could be record-breaking temperatures.
These notices are designed to signal to the electricity market that additional capacity may be required, prompting suppliers to make more power available if necessary.
Such alerts are far more typical during the winter months, when increased demand for heating usually strains the grid.
A spokesman for Neso said: “Our forecasts are showing tight margins on the electricity system for tomorrow evening.
“This is due to the impact of extremely high temperatures affecting Great Britain and the continent and low wind.”
Neso said it was a “routine tool” and stressed that it “does not mean electricity supply is at risk”.
The notice is in effect for the period between 7pm and 10pm on Wednesday.
The extreme heat can put pressure on the electricity system by making processes less efficient, including nuclear power plants, gas stations and water cooling systems.
It also means people are using more electricity for fans and air conditioning to keep cool.
Temperatures could hit 40C on Wednesday and Thursday in some parts of England and Wales as a “heat-dome” settling over western Europe has brought extreme conditions across the continent.
The Met Office has issued a rare red weather warning for extreme heat, which stretches from London across to Somerset and Swansea, and up towards Birmingham, from 9am until 9pm on Thursday.
Transport bosses have urged people to avoid travelling on Wednesday and Thursday and are warning those that do to “prepare for a disrupted journey”.
National Rail warned of disruption to Gatwick Express, Great Northern, Southern and Thameslink services until Friday.
Avanti West Coast said it planned to run fewer services than usual between Tuesday and Thursday, and that there was “a risk of further disruption”.
And Chiltern Railways said it had axed more than half its services until Friday “to ensure the safe operation of the railway”.
Eurostar has cancelled four trains planned to run between London and Paris on Wednesday and Thursday “due to expected adverse weather”.
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