Ummmm, it was policed by management! People whose uniforms smelt of smoke were “counselled” in the same way as they would have been if the uniform was dirty from any other cause.
At first there were on site staff smoking points but these were stopped for two reasons, one the smell on uniforms; and two it was seen as encouraging staff to smoke which wasn’t compatible with a Health Service.
I think its different in mental health facilities, probably harder to stop because of patients smoking. Certainly where I worked, smoking staff were in the minority, so there was less support for smokers.