Although there is a recommended minimum temperature for indoor workplaces there is no similar recommended maximum temperature.
The Approved code of Practice for the Workplace regulations says that the temperature in all workrooms inside buildings shall be reasonably comfortable during working hours without the need to wear special clothing.

The minimum temperature in workrooms should normally be at least 16oC unless much of the work involves severe physical effort in which case the temperature should be at least 13 oC. It’s not always just a matter of temeprature, you may also need to consider other factors such as air movement and relative humidity.

There is no maximum temeprature for workplaces however there may be some exeptions for workplaces such as bakeries, foundries and coldstores where it would be impracticable to maintain these temperatures. However all reasonable steps should be taken to achieve a temperature which is as close as possible to comfortable. The HSE guide to thermal comfort in the workplace says that an acceptable zone of thermal comfort for most people in the UK lies roughly between 13°C (56°F) and 30°C (86°F). But depending on the nature of the work people could suffer at the upper and lower limits.

Where the temperature imight uncomfortably high, for example because of hot processes or the design of the building, reasonable steps should be taken to try and achieve a comfortable temperature,you could look at measures such as insulating hot plant such as boilers and heating pipes, providing air-cooling plant, shading windows by using blinds, screens or films and siting work areas and people away from places subject to radiant heat.

You could also look at local cooling In extremely hot weather fans and increased ventilation may be used instead of local cooling. If conditions are such that workers are still uncomfortable in hot conditions at work you should consider other measures such as job rotation, more frequent breaks and access to cool drinks. In cold conditions suitable protective clothing and rest facilities and provision of hot drinks may be of some help.