Lynsey Mann, GMB health and safety officer, said: “This hot weather is great for being on a sun lounger – but if you’re trying to work through it, it’s no joke. Bosses need to do everything possible to keep workplaces cool, and more importantly, safe.

“This can be as simple as letting people wear more casual clothing and providing proper hydration. High levels of UV exposure also mean that outdoor workers have a much higher risk of developing skin cancer. 

“Simply allowing more breaks and providing sun cream and protective clothing, such as hats with neck covers, can help reduce this risk.

“Ultimately there needs to be a legal maximum working temperature, in the same way we have a legal minimum working temperature. And it is in the employer’s interests – workers who are overheating aren’t going to be at their best.”

Ms Mann also called for employers to supply fans – or the right to expense fans – to employees if they work in a home with excessive temperatures.

She added: “We would also advise members to have extra water, have windows/doors open where possible and shut blinds or curtains.”