The Electricity at Work Regulations 1989 state that lightning protection systems (LPS) should be tested in accordance with the relevant British Standard (which is now BS EN 62305:2011 part 3).

The general industry accepted recommendation used to be that the system is tested at eleven month intervals in order to take account over time all seasonal variations (earth resistance/moisture, temperature, humidity etc).

The recommended maximum interval is now based on the protection level of the system, these are ranked I-IV;

I&II Visual inspection 1 year, Complete inspection 2 years
III & IV Visual inspection 2 years, complete inspection 4 years

‘Critical situation’ systems inspections 1 year (high occupancy buildings, commercial, high rise, sensitive equipment etc)

The protection level of the system is based on a lengthy risk assessment calculation explained in the BSEN and takes into account building fabric, height, strike risk for the area, amongst many others, this is not a straightforward calculation - software is available but it's a specific competence required to get a meaningful solution.

The BSEN further recommends a visual inspection at least annually or more frequently than the above guidelines if the location of the building or the system is exposed to extremes conditions of weather (seemingly everywhere in the UK at present!) or hazardous areas, corrosive atmospheres, high soil corrosion, if the installation components are likely to be subject to mechanical stresses, damage (theft risk of copper) dissimilar metal corrosion, the list could go on and I would stress that it is a risk assessment based approach considering all of the installation factors and requirements of BS EN 62305.

There may be an insurance requirement to fully test annually, in which case the 11month regime would be acknowledged as best practice.

I would also recommend that co-ordinating LPS inspection with the Electrical Inspection and test regime where appropriate would be a good strategy as the two are related.

If you are unsure of the type of system you have or the suitability of the maintenance and inspection regime, consult a competent specialist for advice.

Hope this helps