Ahh..
the old what is COMPETENCE issue again....
DIY domestic electrical work is permitted....
as such a DIY homeowner could add their own fused spur all quite legal and legitimate.
On the same grounds you could install a fused spur quite legitimate and legal...
But if something unforeseen did happen and someone was injured due to your work, you would have to think about how you can prove you were competent and have done everything reasonably practical to ensure the safety of your customers...
Qualifications do not themselves prove this, but they can be one area they helps define competence,
A DIY homeowner can plead ignorance to various aspects of rules and regulations because they are not trained or skilled...
Whereas a person who is doing work as a trade on a daily basis for monetary gain should have a greater awareness and responsibility than a DIY person.
Most competent electricians could show their competence by qualifications, training, having copies of current regulations, having calibrated test equipment, issuing appropriate electrical test certificates for their work, have appropriate business insurance for the type of work they do and possibly by being a member of a recognised trade body.
Basically you need to do your own risk assessment around the work you are doing and what is needed to cover your rear end in the event of a worst case scenario.
Chances are 99% of the time everything is going to be fine...
But it could be argued against you that by either not having suitable qualifications, or getting someone else qualified to fit the spur that you are not showing competence in your work.. ????
:C