EXTREME weather has caused major disruption to the travel network as scores of schools announced closures, with temperatures expected to hit record highs.

A “heat-dome” could bring temperatures of up to 40°C on Wednesday, with this heatwave expected to surpass the June record set in 1976.

A red weather warning covering an area from London to Swansea and Birmingham has been issued by the Met Office from 9am on Wednesday to 9pm Thursday.

Overnight, temperatures are not expected to dip below 20°C at nine locations across England.

The hot weather led to thunderstorms, and the London Fire Brigade received two calls to house fires believed to be caused by lightning strikes.

There has also been severe disruption across London’s transport network, and national rail passengers were urged to avoid non-essential travel due to sagging overhead wires and buckled rails.

Avanti West Coast and Chiltern Railways have reduced services.

Some 100 schools in Somerset will be closed, along with about 100 in Buckinghamshire and 86 in Gloucestershire.

Bledlow Ridge School in Buckinghamshire said it was closing as “classrooms do not have air conditioning,” while Archway School in Gloucestershire said it could not “safely manage the expected extreme temperatures.”

The Department for Education said on Monday that “during hot weather, we don’t normally advise schools to close” and that school leaders should “make sure they take any steps necessary” so that children are “safe and comfortable.”

But the GMB union warned schools to take “immediate action” to protect pupils and staff.

The union has written to the government, calling for enhanced heat controls, reduced heat exposure, lowered physical demand and increased access to water.

GMB national officer Stacey Booth said: “No pupil or member of staff should be expected to learn or work in unsafe levels of heat.

“Once temperatures exceed 30°C, schools should act quickly, use the cooler parts of the building, reduce physical demands, increase water breaks and make sensible adjustments to uniform and duties.

“These are practical steps that can make a real difference. If they can’t be done, school leaders should consider closing parts of the schools.”

The National Association of Head Teachers has issued guidance, with general secretary Paul Whiteman saying that school leaders will “be doing all they can to mitigate the effects.”

Meanwhile, United Nations secretary general Antonio Guterres warned that London is “cooking” as he argued countries cannot double down on fossil fuels.

Speaking at London Climate Action Week, he said: “A climate crisis is pushing us deeper towards higher temperatures and closer to catastrophic tipping points and an energy crisis exposing the folly of a world hooked on hydrocarbons.

“On the surface, these crises may seem separate, but they share the same destructive origin: fossil fuels.”

He warned that climate chaos is “accelerating before our eyes” and that the Middle East war has “unleashed the mother of all energy shocks.”

Mr Guterres said the twin crises “demand the same answer” — namely, a “fast, fair transition to clean energy and a surge in adaptation, resilience and climate justice for those already facing climate harm.”