The above is the correct British Standard, but it was also published in 1999. Use that version.
The Fire Protection Association publish "RC35 Recommendations for the protection of buildings against lightning strike" This lists the other European and US standards and other stuff if you really want details.
As a simple rule of thumb:
Is the building one where large numbers congragate, significants amounts of explosives or flammables are kept, tall, isolated, or of significant or cultural importance? If yes then you need lightning protection, if you are unsure, then refer to the risk assessment contained within the BS. Be warned, it's not easy. Different parts of Britain get struck more often, for example Kent gets more than most areas.
Don't forget surge protection too, that's different but necessary to protect electrical systems.
Lightning protection needs annual checks.
Your insurers might require lightning protection, it's not normally part of a fire risk assessment.
