(A) Fixed wiring
All fixed wiring installations and related equipment should be installed and maintained by a competent person.
In general, at a commercial premise, it is recommended (IEE Wiring Regs BS7671) that a fixed wiring installation be tested at least every 5 years. However premises where risks are higher i.e. industrial establishments or leisure facilities, the frequency will be increased.
The Electrical Safety and your Business leaflet provides information on the recommended frequency for ensuring the fixed wiring is inspected to ensure it is safe to be in use.
(B) PAT (portable appliance testing)
It is recommended that all electrical appliances are examined/checked ("PAT" Tested) at a frequency appropriate to the risk.
Not every electrical item needs a portable appliance test (PAT). In some cases, a simple user check and visual inspection is enough, e.g. checking for loose cables or signs of fire damage and, if possible, checking inside the plug for internal damage, bare wires and the correct fuse. Other equipment, e.g. a floor cleaner or kettle, may need a portable appliance test, but not necessarily every year.
As of the 2nd of May 2012 new guidance was issued and the link below takes you to the latest guidance from the HSE regarding PAT testing to avoid businesses wasting valuable time and money on unnecessary tests; https://www.hse.gov.uk/pubns/indg236.pdf.
Regular maintenance should include visual checks for general wear and tear ensuring that plugs, leads and sockets are in good condition and that there is no exposed wiring.
Where appropriate, industrial type plugs and sockets should be used as these are more robust and can stand up to the conditions better. Working areas should have sufficient socket outlets to avoid trailing cables. Any corrective actions must be carried out immediately.