New2. It's very simple.
All electrical installation work requires a certificate (Electrical Installation Certificate - EIC). That is (and has been for many, many years) a requirement of the wiring regulations.
In addition, since Jan 1 2005, electrical installations in dwellings have come under the scope of Part P of the building regulations. The majority of such work is notifiable to local authority building control (LABC).
The EIC certifies that work has been carried out to BS7671.
The building regs notification certifies that the job not only complies to BS 7671 (or equivalent) but also complies with all other applicable building regulations.
Your FOAF has issued an installation certificate, but has clearly not notified LABC of the work. It is quite possible, as Pensdown has suggested, that he is not a member of a scheme that allows him to self-certify. But even if he is so registered, whilst he may still issue an EIC, he cannot notify the work of others under his self-certification registration.
So, you still need to notify this work, in which case you need to enquire about 'regularisation' - a retrospective means of gaining building regulations approval. Contact your local authority building control office, explain what work was done and that you have a test certificate. Then do what they tell you.