Part P Regulations came into force on 1st January 2005. Until that date there was no requirement for electrical work for satisfy Building Regulations other than a competent person must do the work. Since 1st January 2005 certain work either requires a Building Control application to enable the work to be checked by a qualified person or the person doing the work must be certified as able to sign-off his/her own work.
Since Building Regulations are not retrospective, unless the person doing the work did it after January 2005, or he/she could not be regarded as a competent person, the situation will not arise.
There was no test of a competent person - it was about following the codes and standards recommended by the IEE and others for electrical installations