The adequacy of earthing and bonding.
The suitability of the switchgear and controlgear. For example, an old fusebox with a wooden back, cast-iron switches, or a mixture of both will need replacing.
The serviceability of switches, sockets and lighting fittings. Items that  may need replacing include: older round-pin sockets, round light switches, cables with fabric coating hanging from ceiling roses to light fittings, black switches and sockets mounted in skirting boards.
The type of wiring system and its condition. For example, cables coated in black rubber were phased out in the 1960s. Likewise cables coated in lead or fabric are even older and may well need replacing (modern cables use longer-lasting pvc insulation).
Sockets that may be used to supply portable electrical equipment for use outdoors, making sure they are protected by a suitable residual current device (RCD).
The presence of adequate identification and notices.
The extent of any wear and tear, damage or other deterioration.
Any changes in the use of the premises that have led to, or may lead to, unsafe conditions.
The competent person will then issue an Electrical Installation Condition Report detailing any observed damage, deterioration, defects, dangerous conditions and any non-compliances with the present-day safety standard that might give rise to danger.
If any dangerous or potentially dangerous condition or conditions are found, the overall condition of the electrical installation will be declared to be ‘unsatisfactory’, meaning that remedial action is required without delay to remove the risks to those in the premises.