It's not as if winter doesn't come every year, so employers should be anticipating possible problems. If a workshop is cold, then a simple loss of your grip could mean the loss of your finger. Or, in an office, a cold environment could mean a loss of concentration for the staff. So not providing a good working temperature to save a few pennies could cost the boss dearly.
Plus of course your employer would be breaking the law by letting the temperature drop. There is a minimum temperature below which your employer needs to take action, or send you somewhere warmer (like home). The law on minimum temperatures is clear and unambiguous – at least 13oC for workplaces where strenuous work is carried out, and 16oC generally.