What should be maintained?

In order to prevent danger, all electrical equipment and systems should be maintained on a regular basis. Each and every piece of electrical equipment must be examined and tested according to the IEE Code of Practice recommendations. This includes equipment both permanently connected, and equipment connected by a plug to a socket outlet.
All electrical systems and equipment should be maintained if danger would otherwise arise. Other than the fixed installation, all electrical equipment in an installation, whether permanently connected or connected by a plug and socket outlet, should be inspected and tested in accordance with the recommendations contained in the IEE Code of Practice.
Also, “BS 7671: Requirements for Electrical Installations” insists that a fixed installation be examined and tested for safety on a periodic basis.