Businesses are being urged to relax dress codes and provide ample water for staff as England swelters through its third heatwave of the summer.
The conciliation service Acas issued the advice after research showed half of workers felt poor sleep due to heat impacted their job.
One in five also cited overheated offices and maintaining focus as major challenges.
Temperatures are set to exceed 31C in some areas on Friday.
Acas chief executive Niall Mackenzie said: “The sizzling weather may be ideal for the beach, but staff getting into work during one of the hottest weeks of the year may not feel the same way.
“Some employees with certain health conditions or disabilities may be adversely affected by the extreme heat. The heat can also impact public transport too which can affect employees commuting into work.”
“Acas has some top tips for employers to help ensure their businesses remain productive during the heatwave whilst keeping staff happy too.”
Acas suggested keeping workplace temperatures reasonable, keeping fans or air conditioning switched on, providing staff with drinking water, allowing extra breaks for cold drinks, and relaxing the rules for wearing ties or suits.
Saturday is set to be the hottest day of the week in England, with London potentially reaching 33C and high UV and pollen counts across much of the country, before a similarly hot day on Sunday with temperatures forecast between 27 and 31C.
Earlier this week, Greece imposed mandatory work breaks in parts of the country where temperatures were expected to exceed 40C.
The Labour Ministry ordered the work stoppage, from midday to 5pm, for outdoor manual labour and food delivery services. Employers were also asked to offer remote work options.
South Korea’s government has also announced it will require outdoor workers to take a mandatory 20-minute break every two hours during heatwaves, in a move aimed at tackling rising heat-related deaths.
The rule, expected to take effect next week, applies to construction, landscaping, delivery, and other outdoor occupations.
The mandate will come into effect whenever the temperature reaches 33C.
