Campaigners are warning of “worryingly hot” temperatures affecting children and teachers in classrooms as climate change drives more heatwaves.

The warning comes after research showed classrooms breached a recommended maximum temperature of 26C during the recent heatwave in late June.

A study by climate campaign group Round Our Way worked with teachers in seven schools across England to put sensors in classrooms that recorded the temperature automatically every hour over a period of four weeks.

The period included the late June heatwave, when the UK’s Health Security Agency (UKHSA) issued a yellow heat health alert for most of England as temperatures climbed to 30C.

The data found that, while there is no legal maximum temperature for schools or workplaces, temperatures in six of the seven schools exceeded the 26C maximum which is advised by the National Education Union (NEU).

The highest peak indoor temperature recorded was in Cambridgeshire, with 29.6C in the classroom by the end of the school day, while schools in West Sussex and Suffolk recorded peaks of 28.3C and 28.2C respectively.

Roger Harding, director of Round Our Way, which describes itself as a not-for-profit supporting people impacted by climate change in the UK, said: “This data reveals the worryingly hot temperatures our children are starting to face in the classroom thanks to climate change.

“Hard-pressed teachers have told us about children this summer who have fainted or even vomited due to the high heat, and there are many more who simply struggle to concentrate.

“This has been a mild summer by recent standards, so it is scary to picture how bad this will get when temperatures well above 30°C return.”

He warned that schools, like many of the UK’s buildings, were not set up and funded to deal with the higher temperatures being seen because of climate change.

“The weather used to just be small talk but we now need our political leaders to ensure the country is better prepared for more extreme weather and to tackle the fossil fuel pollution that is causing it in the first place,” he said.

It comes after analysis from the Met Office shows the UK is seeing, on average, more frequent periods of hot weather and an increase in extreme rainfall, bringing challenges for infrastructure, health and wellbeing.

But the Government’s plan to adapt to the risks posed by climate change is currently being challenged in the High Court, by campaigners who claim the Tory administration’s July 2023 National Adaptation Programme (NAP) fails to properly respond to 61 climate change risks.