Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 22. The Principle of Precautions against the Effects of Attacks
The UK LOAC Manual (2004) states:
Parties to a conflict are required, to the maximum extent feasible, to:
c. take other necessary precautions to protect the civilian population, individual civilians and civilian objects under their control against the dangers resulting from military operations. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.36.
In its chapter on internal armed conflict, the manual states:
15.24. Military commanders and the civilian authorities should do everything that they feasibly can do to protect civilians and civilian objects in their area of control from the effects of war.
15.24.1. Nothing is laid down in customary law or in the treaties dealing with internal armed conflicts about precautions in defence. This is a matter of common humanity. The use of human shields is prohibited. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 15.24–15.24.1.
At the CDDH, the United Kingdom
expressed keen satisfaction at the adoption of [Article 58 of the 1977 Additional Protocol I], which was designed to lend added strength to the protection already extended to civilian persons and objects of a civilian character by preceding articles. Nevertheless, in an armed conflict such protection could never be absolute; and that was reflected in the article through the expression “to the maximum extent feasible”. According to the interpretation placed upon it by [the United Kingdom], the word “feasible”, wherever it was employed in the Protocol, related to what was workable or practicable, taking into account all the circumstances at a given moment, and especially those which had a bearing on the success of military operations. 
United Kingdom, Statement at the CDDH, Official Records, Vol. VI, CDDH/SR.42, 27 May 1977, p. 214, §§ 58–59.
Upon signature of the 1977 Additional Protocol I, the United Kingdom stated: “The word ‘feasible’ means that which is practicable or practically possible, taking into account all circumstances at the time including those relevant to the success of military operations.” 
United Kingdom, Declarations made upon signature of the 1977 Additional Protocol I, 12 December 1977, § b.
Upon ratification of the 1977 Additional Protocol I, the United Kingdom stated that it understood the term “feasible” as used in the Protocol to mean “that which is practicable or practically possible, taking into account all circumstances ruling at the time, including humanitarian and military considerations”. 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § b.