According to section 443.4 of the 18th edition UK wiring regulations (BS 7671:2018) . . .
“Protection against transient overvoltages shall be provided where the consequence caused by overvoltage could:
(i) result in serious injury to, or loss of, human life, or
(ii) result in interruption of public services and/or damage to cultural heritage, or
(iii) result in interruption of commercial or industrial activity, or
(iv) affect a large number of co-located individuals.
For all other cases, a risk assessment according to Regulation 443.5 shall be performed in order to determine if protection against transient overvoltages is required. If the risk assessment is not performed, the electrical installation shall be provided with protection against transient overvoltages, except for single dwelling units where the total value of the installation and equipment therein does not justify such protection. Protection against switching overvoltages shall be considered in the case of equipment likely to produce switching overvoltages or disturbances exceeding the values according to the overvoltage category of the installation eg where an LV generator supplies the installation or where inductive or capacitive loads (eg motors, transformers, capacitor banks), storage units or high-current loads are installed.”