1. Where Article 88 is complied with, insurance and reinsurance undertakings may calculate the sum insured for windstorm risk referred to in point (b) of paragraph 6, and in paragraph 7, of Article 121 on the basis of groups of risk zones. Each of the risk zones within a group shall be situated within one and the same particular region set out in Annex V. Where the sum insured for windstorm risk referred to in point (b) of Article 121(6) is calculated on the basis of a group of risk zones, the risk weight for windstorm risk referred to in point (a) of Article 121(6) shall be the risk weight for windstorm risk in the risk zone within that group with the highest risk weight for windstorm risk set out in Annex X.