The Workplace (Health, Safety and Welfare) Regulations 1992 state thatThat is generally taken to mean between 16C (61F) and 24-25C (75F). If your work involves physical labour, then that lower temperatire may be 13C. There used to be a minimum (16C IIRC) that was actually defined but that legislation has now been superceded. You are also entitled to sufficient ventilationDuring working hours, the temperature in all workplaces inside buildings shall be reasonable.
.6.—(1) Effective and suitable provision shall be made to ensure that every enclosed workplace is ventilated by a sufficient quantity of fresh or purified air.