Since 1980 it has been a legal requirement that if you are an employer with people working for you who uses or has access to electrical equipment owned by you you must have proof that it is reguarly inspected and is safe to use. PAT testing and the associated papperwork is one way of proving this.

I am constantly dismayed that so fiew employers are aware of this.

If you are self-employed you are your own employer so this law also involves you.

PAT testing could be looked on as "voluntary" but if your plug-in appliances are unsafe when in use and someone is injured, the law and any involved insurance companies will rather unkindly on you.

PAT tests or Portable Appliance Testing tests cover any appliances that plug into a socket of any voltage, including extention cables, plug adaptors, power supplies for laptops, amps, and lighting rigs.