The Health & Safety Executive provides no set rule on PAT testing frequency, only that testing should be done regularly to ensure preventative maintenance. The reason that there is no set frequency is because different situations arise that call for different measures. There are a number of factors that affect PAT testing frequency and it is up to each individual to determine when testing should be carried out.
Best practice suggests annually and this is a requirement for HMO’s. We do ours annually or at change of occupancy, whichever comes first for any of our properties that have appliances. This satisfies that we are carrying out regular inspections and therefore covers the above. The requirement and frequency is different for Schools, shops etc. and in construction 110V equipment is required to be tested every 3 months. Hope this helps.