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All employers who have staff working in inclement conditions should have suitable control measures in place to ensure the health, safety and welfare of those personnel.

Risk assessment(s) should have not only identified any risks involved in the work process, site situation and operation but also any risks arising out of exposure to weather, which can cause problems of too hot, too cold, too wet, snow, ice and of course UV radiation.
 
Personal protective equipment (PPE) should be provided and the type and amount has to be appropriate to the possible risks. You may need to provide shelter where staff can warm-up/dry out especially in adverse winter conditions. This should form part of the elimination or minimising of the risk considered by the risk assessment.
 
If you do not have a proper health and safety policy in place supported by risk assessments, and all the other requirements of health and safety regulations, you need to act immediately.
 
You might also wish to consider that an employer who looks after the welfare of employees benefit thereby.