Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 13. Area Bombardment
The UK LOAC Pamphlet (1981) stipulates that “area bombardment is an example of an indiscriminate attack” and is, as such, prohibited. 
United Kingdom, The Law of Armed Conflict, D/DAT/13/35/66, Army Code 71130 (Revised 1981), Ministry of Defence, prepared under the Direction of The Chief of the General Staff, 1981, Section 4, p. 15, § 5(j).
The UK LOAC Manual (2004) states:
The following are examples of indiscriminate attacks:
a. “an attack by bombardment by any methods or means which treats as a single military objective a number of clearly separated and distinct military objectives located in a city, town, village or other area containing a similar concentration of civilians or civilian objects”. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 5.23.2.
In 2003, during a debate in the House of Commons, the UK Secretary of State for Defence stated:
Coalition operations are clearly continuing. I made that clear in my statement, and I do not think that any Member of the House would expect me to anticipate the nature of those operations save to say that whatever targets are addressed will be targets associated with Saddam Hussein’s regime. I made that clear yesterday to the House, and I repeat it again today. We will not engage in indiscriminate so-called carpet bombing. Each of the targets will be individually addressed and attacked. 
United Kingdom, House of Commons, Statement by the Secretary of State for Defence, Hansard, 21 March 2003, Vol. 401, Debates, cols. 1214–1215.