It is recommended that you have your electrical installation at home is checked every 10 years. The extent of the inspection is entirely up to you but you should discuss your options with the electrician. A full and extensive inspection is highly recommended if your installation is in excess of 25 years old. This is because the life of cables, on average, is about 25 years and they may be starting to breakdown. Furthermore, no matter how clean you keep your house, you will find insects of various kinds, dust and possible dampness behind switches and plug sockets,
If you installation is particularly old, you may find cables in the cavity of the building. If you have then had cavity insulation it will be found that the cables are being attacked by the insulation. Loft insulation is another culprit for affecting cables. Additional insulation is usually laid on top of cables and other electrical items in the loft. This all goes to downgrade the cable current carrying capacity and if you have transformers in the loft, for extra low voltage lights etc, these will become hot and break down.
Periodic Inspection & Testing takes the form of both visual inspection and physical testing of the installation. Visual inspection involves looking at accessories, accessible cables, checking connections. The purpose of this is to see if there is any damage and that everything is compliant with current regulations. It is also to check that there is adequate protection of individual circuits.
Physical testing checks the continuity of circuits in all conductors, insulation of circuit cables and accessories, polarity, trip times of RCD's if fitted and functional testing of equipment. The earthing to the property will also be checked to verify it is adequate.
The test results and observations will be recorded in a report that will be given to you.