Comfort at work
It's not just about complying with regulations. A comfortable workplace or retail environment makes economic sense.
An overly hot or cold environment can have a significant effect on productivity, lead to low staff morale, increase staff turnover and cause customer discomfort.
Regulation 7 of The Workplace (Health, Safety and Welfare) Regulations 1992 deals specifically with indoor workplaces temperature.
Further information:
https://www.hse.gov.uk/contact/faqs/temperature.htm
https://www.hse.gov.uk/temperature/thermal/index.htm