Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 42. Works and Installations Containing Dangerous Forces
Section A. Attacks against works and installations containing dangerous forces and against military objectives located in their vicinity
The UK LOAC Pamphlet (1981) states that it is prohibited “to attack dykes, nuclear power stations or dams if to do so would cause the release of dangerous forces and consequent severe losses among the civilian population, unless they are used in direct support of military operations or for military purposes”. 
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(i).
The UK LOAC Manual (2004) states:
5.30. Dams, dykes and nuclear electrical generating stations “shall not be made the object of attack, even where these objects are military objectives, if such attack may cause the release of dangerous forces and consequent severe losses among the civilian population.” “Other military objectives located at or in the vicinity of these works or installations shall not be made the object of attack if such attack may cause the release of dangerous forces from the works or installations and consequent severe losses among the civilian population.”
5.30.3. The United Kingdom, on ratification of Additional Protocol I, declared that:
The United Kingdom cannot undertake to grant absolute protection to installations which may contribute to the opposing Party’s war effort, or to the defenders of such installations, but will take due precautions in military operations at or near the installation … in the light of the known facts, including any special markings which the installation may carry, to avoid severe collateral losses among the civilian population; direct attacks on such installations will be launched only on authorisation at a high level of command.
5.30.4. Attacks only become unlawful if they may result in the release of dangerous forces and consequent severe losses among the civilian population …
5.30.5. In certain exceptional circumstances the protection afforded to dams, dykes and nuclear electrical generating stations ceases:
a. “for a dam or dyke only if it is used for other than its normal function and in regular, significant and direct support of military operations”;
b. “for a nuclear electrical generating station only if it provides electric power in regular, significant and direct support of military operations”;
c. “for other military objectives located at or in the vicinity of” dams, dykes and nuclear electrical generating stations “only if they are used in regular, significant and direct support of military operations”;
and, in the case of a, b, and c, “if such attack is the only feasible way to terminate such support.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 5.30 and 5.30.3–5.30.5.
With regard to internal armed conflict, the manual states:
15.21. In accordance with the general principles of targeting set out above, objects such as dams, dykes, and nuclear power stations which contain forces, the escape of which would be likely to endanger the civilian population, may only be attacked if they (a) constitute military objectives and (b) care is taken to minimize the risk to the civilian population. The latter requirement is of special importance with such targets because of the danger that they can pose.
15.21.1. The protection given to these objects in international conflicts is much more detailed. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 15.21–15.21.1.
With regard to internal armed conflicts in which the 1977 Additional Protocol II is applicable, the manual specifies:
15.51. It is forbidden to attack dams, dykes and nuclear electrical generating stations “even where these objects are military objectives, if such attack may cause the release of dangerous forces and consequent severe losses among the civilian population”.
15.51.1. This would not, however, prevent an attack on a nuclear, chemical or bacteriological research centre, even though such an attack might release dangerous forces, provided that the attack was not made illegal by some other provision of the Protocol. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, §§ 15.51–15.51.1.
In its chapter on enforcement of the law of armed conflict, the manual notes:
Additional Protocol I extends the definition of grave breaches to include the following:
b. any of the following acts, when committed wilfully, in violation of the relevant provisions of the protocol, and causing death or serious injury to body or health:
(3) launching an attack against works or installations containing dangerous forces in the knowledge that such attack will cause excessive loss of life, injury to civilians or damage to civilian objects. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.25.
The UK Geneva Conventions Act (1957), as amended in 1995, punishes “any person, whatever his nationality, who, whether in or outside the United Kingdom, commits, or aids, abets or procures the commission by any other person of, a grave breach of … [the 1977 Additional Protocol I]”. 
United Kingdom, Geneva Conventions Act, 1957, as amended in 1995, Section 1(1).
In 1986, in reply to a question in the House of Lords, the UK Minister of State for Defence Procurement declared:
Existing laws of war already impose restrictions on attacks on [nuclear] installations which would pose a particular threat to civilian populations and require a balance to be struck between the military advantage and the danger of collateral damage to the civilian population. 
United Kingdom, House of Lords, Statement by the Minister of State for Defence Procurement, Hansard, 10 June 1986, Vol. 476, col. 112.
In 1991, in reply to a question in the House of Lords concerning “the position in international law relating to the use of ‘conventional’ weapons against (a) nuclear facilities, (b) chemical weapons plants and dumps, and (c) petrochemical enterprises situated in towns or cities, when such use may release radioactivity, toxic chemicals, or firestorms, on a scale comparable to the use of nuclear, chemical, and other weapons deemed to be weapons of mass destruction,” the UK Minister of State, Foreign and Commonwealth Office, stated:
International law requires that, in planning an attack on any military objective, account is taken of certain principles. These include the principles that civilian losses, whether of life or property, should be avoided or minimised so far as practicable, and that an attack should not be launched if it can be expected to cause civilian losses which would be disproportionate to the military advantage expected from the attack as a whole. 
United Kingdom, House of Lords, Statement of the Minister of State, Foreign and Commonwealth Office, Hansard, 4 February 1991, Vol. 525, Written Answers, col. 37.
In 1993, in reply to a question in the House of Lords as to whether the bombing of nuclear facilities in Iraq was concordant with international law, the UK Minister of State, Foreign and Commonwealth Office, wrote that “the then Prime Minister condemned the Israeli bombing of Iraqi nuclear facilities as a grave breach of international law”. 
United Kingdom, House of Lords, Reply of the Minister of State, Foreign and Commonwealth Office, Hansard, 31 March 1993, Vol. 544, Written Answers, col. 53.
In 1991, the UK Secretary of State for Defence, responding to questions in the Defence Committee concerning the United Kingdom’s participation in bombing nuclear reactors during the Gulf War, declared that the attack was undertaken “with the very greatest care and after the most detailed planning to minimise the risk of any contamination or the risk of any radiation spreading outside the site”. He went on to say that he was “not aware of any evidence that there was a risk of any contamination outside the site which would tend to suggest that those were very precise and very carefully planned attacks”. 
United Kingdom, Statement by Secretary of Defence before the Defence Committee, Minutes of evidence, 6 March 1991, Report on UK Practice, 1997, Chapter 1.9.
Upon ratification of the 1977 Additional Protocol I, the United Kingdom stated with respect to Articles 56 and 85(3)(c):
The United Kingdom cannot undertake to grant absolute protection to installations which may contribute to the opposing Party’s war effort, or to the defenders of such installations, but will take all due precautions in military operations at or near the installations referred to in paragraph 1 of Article 56 in the light of the known facts, including any special marking which the installation may carry, to avoid severe collateral losses among the civilian population; direct attacks on such installations will be launched only on authorisation at a high level of command. 
United Kingdom, Reservations and declarations made upon ratification of the 1977 Additional Protocol I, 28 January 1998, § n.