BS EN 62305

BS EN 62305 is the latest reference document for protection against lightning. It replaced BS 6651:1999 from 1st September 2008. It is the British edition of the European standard to which all lightning protection systems to new structures, and new extensions to existing ones, are now designed, installed and maintained. BS EN 62305 comprises four parts and these detail the fundamental requirements for lightning protection systems for the external and internal parts of a structure. The four parts are as follows:
Part 1: General principles
Part 2: Risk management
Part 3: Physical damage to structures and life hazard
Part 4: Electrical and electronic systems within buildings.

BS EN 62305-1 provides the general principles to be followed in the protection of structures against lightning, including their installations and contents as well as people.

BS EN 62305-2 is applicable to risk assessment for a structure due to lightning flashes. Its purpose is to provide a procedure for the evaluation of such a risk.

BS EN 62305-3 provides the requirements for protection of a structure against physical damage by means of a lightning protection system (LPS), and for protection against injury to living beings due to touch and step voltages in the vicinity of an LPS.

Doesn't answer your question about height but I looked into thios some time ago. other considerations where lighting protection might be required includes:

Where large numbers of people congregate .
Where essential public services are concerned.
Where the area id one where lighting is prevelent.
Where there are very tall isolated structures.
Structures of historic or cultural importance.
Structures with explosive or flammable contents.