Соответствующая норма
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 54. Attacks against Objects Indispensable to the Survival of the Civilian Population
Section C. Attacks in case of military necessity
The UK LOAC Manual (2004) states:
In cases of imperative military necessity, a party to the conflict may depart from the prohibition relating to indispensable objects in order to defend its national territory from invasion, but only in those parts of its territory that are under its control. The exception for the defence of national territory might include, for example, the flooding of low-lying areas to impede invading forces. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.19.