Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 2. Violence Aimed at Spreading Terror among the Civilian Population
The UK LOAC Manual (2004) states: “Acts or threats of violence, the primary purpose of which is to spread terror among the civilian population are prohibited.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.21.
In its chapter on internal armed conflict, the manual further states: “Attacks aimed at terrorizing civilians are prohibited.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.8.
At the CDDH, the United Kingdom voted in favour of Article 46 of the draft Additional Protocol I (now Article 51), describing its first three paragraphs as containing a “valuable reaffirmation of existing customary rules of international law designed to protect civilians”. 
United Kingdom, Statement at the CDDH, Official Records, Vol. VI, CDDH/SR. 41, 26 May 1977, p. 164, § 119.