Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 147. Reprisals against Protected Objects
Section F. Works and installations containing dangerous forces
The UK LOAC Pamphlet (1981) provides: “The Geneva Conventions and [the 1977 Additional Protocol I] prohibit reprisals against … works containing dangerous forces”. 
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. 17, § 16.
The UK LOAC Manual (2004) states:
16.19. Additional Protocol I extends the categories of persons and objects against whom reprisals are prohibited to:
f. works or installations containing dangerous forces, namely dams, dykes and nuclear electrical generating stations. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.19.
The manual also restates the interpretative declaration made by the UK upon ratification of the 1977 Additional Protocol I. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.19.1.
The manual explains:
This means that reprisals taken in accordance with the statement are permissible by and against the United Kingdom. However, commanders and commanders-in-chief are not to take reprisal action on their own initiative. Requests for authority to take reprisal action must be submitted to the Ministry of Defence and require clearance at Cabinet level. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 16.19.2.
In its written statement submitted to the ICJ in the Nuclear Weapons case in 1995, the United Kingdom stated:
To be lawful, a belligerent reprisal must meet two conditions. First, it must not be directed against persons or objects against which the taking of reprisals is specifically prohibited … Additional Protocol I prohibits the taking of reprisals against … works and installations containing natural forces (Article 56(4)). The application of these provisions would have a greater effect on the retaliatory use of nuclear weapons. Again, however, these provisions are correctly regarded as innovative and thus as inapplicable to the use of nuclear weapons. 
United Kingdom, Written statement submitted to the ICJ, Nuclear Weapons case, 16 June 1995, pp. 58–59.