Darkwood.
It is a statutory requirement (unlike the requirements of BS7671) that any worker whether they be a cleaner or an electrician, should be so experienced, qualified or under such supervision that they would satisfy the BS7671 definition of a skilled or instructed person.
If that cleaner or electrician does not satisfy the BS7671 definition of a skilled or instructed person, the employer will be committing a criminal act by allowing them to work with electricity, even if that work only involves plugging in a hoover.
A skilled or instructed person does not have to be supervised when using socket-outlets, in fact the cleaner would be considered as someone who could do the supervision.
You may believe that the cleaner is not a skilled or instructed person.
However BS7671 disagrees.
It does seem yo me, to be a very common misconception that a skilled person has to be a qualified electrician, and an instructed person has to be an electrical Apprentice.
The fact is, a skilled person can be anyone with sufficient experience or training, to know that they should not plug in a hoover with a damaged lead.
An instructed person can be someone with access to a skilled person via a telephone.