(2-part post):
The only official 'policies' relate to the same Health & Safety regulations that apply to other types of employment.
The employer must carry out a risk assessment for the job (taking into account that the employee will be working alone at night). For each activity to be carried out, this should state the risk of an accident (or, for example, of an assault by a customer) assessed on a scale of 1 (low) to 4 (high) together with the likely seriousness of any injury occurring because of such an accident (or assault). (This is also assessed on a scale of 1 to 4). The assessment must then state the control measures, put in place by the employer, to minimise the risk of such incidents occurring. The employer must make the risk assessment available to the employee.
For some occupations, the risk factors would be fairly low. e.g. someone sitting in a secure office throughout the night, handling emergency calls for a group of doctors, would probably not be assessed as being greatly at risk.