It's the old faithful, the frequently asked question when the UK hits its 'heatwave'!

Q. What is the maximum/minimum temperature in the workplace?

The Workplace (Health, Safety and Welfare) Regulations 1992 lay down particular requirements for most aspects of the working environment

Regulation 7 of these Regulations deals specifically with the temperature in indoor workplaces and states that:

During working hours, the temperature in all workplaces inside buildings shall be reasonable. However, the application of the regulation depends on the nature of the workplace i.e. a bakery, a cold store, an office, a warehouse.

The associated ACOP goes on to explain:

'The temperature in workrooms should provide reasonable comfort without the need for special clothing. Where such a temperature is impractical because of hot or cold processes, all reasonable steps should be taken to achieve a temperature which is as close as possible to comfortable. 'Workroom' means a room where people normally work for more than short periods.

The temperature in workrooms should normally be at least 16 degrees Celsius unless much of the work involves severe physical effort in which case the temperature should be at least 13 degrees Celsius. These temperatures may not, however, ensure reasonable comfort, depending on other factors such as air movement and relative humidity.'

You can read more about controlling workplace temperature and tips to keep your cool on the website in the A-Z -  'Temperatures in the Work place'.

(source - The Workplace (Health, Safety and Welfare) Regulations 1992 and associated ACOP)