There's an article here
http://www.landlordzone.co.uk/pdf/3-...y%20Checks.pdf

There's no legal requirement for any particular checks to be carried
out, nor any requirement for how often checks should be carried out -
however, should something go wrong, you need to be able to prove due
diligence.

one way of supporting due diligence would be to carry out some testing.
Frequency of testing also varies with whether the product is portable
or not - that is fitted with a plug, rather than hard-wired to a fused
spur - as the flex on a portable prodcut is assumed to be more at risk
of damage.

You should also provide complete instructions for the use of all
electrical appliances in the property. That way the tenant can
familiarise themselves with the specific warnings in user manuals
(which often include instructions aimed only at the terminally stupid).

Charlie