is there a union where you are?
I remember when I was temping at the council lots of people wanted to go home because it was too hot in the building and they sent the Union Rep round to me (I was working for the department head) with a complaint... unfortunately there is no upper limit but the lower limit is something like this (found that when I was researching and it's a union text, so not 100% sure about its accuracy)
Hope this helps
The Workplace Health, Safety & Welfare Regulations 1992 sets out minimum temperatures and states quite clearly that during working hours the temperature in all workplaces inside buildings shall be reasonable. (Reg.7 ACOP 43 ?temperatures 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 a least 13 degrees celsius???)