there is no general legal prohibition on lone working but the broad duties of the HASAWA 1974 and MHSWR 1999 still apply, these require identfying hazards of the work,assessing the risks involved and putting measures in place to avoid or control the risks.
there are some high risk activities where at least one other person may need to be present...i:e ..confined space working where a supervisor may need to be present as well as a someone dedecated to the rescue role.
But employers need to be aware of specific law on lone working applying in thier industry....i.e........Diving operations, fumigation work.
Establishingsafe working for lone workers is no different from organising the safety of other employees.
Employers need to know the law and standards which apply to their work activities and then assess whether the requirements can be met by people working alone.
by the way you can get lone worker alarms which are normally triggered if are horizontal for more than 20 secs or so.
HASAWA 1974( the health and safety at work act 1974.)
It SHALL (which in law means MUST) be the duty of every employer to ensure,so far is as resonably practicable,the health,safety and wefare at workof all his employees.