Interestingly, although the law specifies minimum values below which workplace temperatures must not fall, it only requires a "reasonableness" test as far as high temperatures are concerned.

The minimum workplace temperature for sedentary (ie. desk based) jobs is 16 degrees celcius with a lower minimum of 13 degrees for jobs where some form a physical activity is involved (ie. working in a warehouse).

At the upper end of the scale an employee with a thermometer (!) can't demand to go home when a certain temperature is hit, although you do need to make sure that as an employer you apply the "reasonable" criteria sympathetically. Excessively high temperatures are likely to affect the performance of your team and therefore for this reason alone you need to take steps to cool their working environment.

If you get a complaint about working in excessive heat – particularly from those whom the heat may affect more than others such as your older team members or pregnant workers – then it is advisable to put in place temporary measures to alleviate the situation. This might include increasing ventilation in the workplace or hiring in fans or air con units.

If there is a "serious and imminent" danger to your employees health then they do have the right to down tools, although in an average British summer you are not likely to be faced with this particular situation. Therefore, a common sense approach to high workplace temperature should stand you in good stead and ensure the continued smooth running of your business.