Is it the same way for Commercial and Industrial work as well?
From a practical perspective, an industrial contract is most likely going to insist that anyone carrying out the installation is accredited to appropriate standards.
From a legal standpoint, however, I'm aware of nothing which restricts who can carry out the work. The Health & Safety at Work Act kicks in on commercial properties, but that only specifies the standard to which work must be carried out. There's nothing about who may or may not do the work. As far as I can see, if you could train a monkey to install the equipment it would be perfectly legal so long as it meets the appropriate standard afterward.
When it comes to small commercial premises (village shops and the like), a lot of owners will DIY their own electrics, and it's perfectly legal, so long as the requisite HSE standards are met.
