Related Rule
United Kingdom of Great Britain and Northern Ireland
Practice Relating to Rule 75. Riot Control Agents
The UK LOAC Manual (2004) provides in its chapter on weapons: “States party [to the 1993 Chemical Weapons Convention] undertake not to use riot control agents as a method of warfare.” 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 6.8.2.
In its chapter on internal armed conflict, the manual prohibits the use of “chemical weapons, including riot control agents, as a method of warfare”. 
United Kingdom, The Manual of the Law of Armed Conflict, Ministry of Defence, 1 July 2004, § 15.28.
In 1931, in a memorandum submitted to the League of Nations Preparatory Commission for the Disarmament Conference, the UK Government stated:
Basing itself on this English text [of the 1925 Geneva Gas Protocol], the British Government have taken the view that the use in war of “other gases”, including lachrymatory gases, was prohibited. They also considered that the intention was to incorporate the same prohibition in the present Convention [i.e. in a draft convention on disarmament discussed at the Preparatory Commission]. 
United Kingdom, Memorandum by the UK Delegation to the League of Nations Preparatory Commission for the Disarmament Conference, reprinted in League of Nations Doc. C.4.M.4. 1931, IX, Documents of the Preparatory Commission for the Disarmament Conference, Series X, Minutes of the Sixth Session (Second Part), 15 January 1931, p. 311.
Canada, China, Czechoslovakia, Japan, Romania, Spain and the Socialist Federal Republic of Yugoslavia were among the States which expressly associated themselves with the UK memorandum. 
Canada, China, Czechoslovakia, Japan, Romania, Spain and Socialist Federal Republic of Yugoslavia, Statements before the League of Nations Preparatory Commission for the Disarmament Conference, 15 January 1931, League of Nations Doc. C.4.M.4. 1931, IX, Documents of the Preparatory Commission for the Disarmament Conference, Series X, Minutes of the Sixth Session (Second Part), 15 January 1931, p. 311.
In 1970, in reply to a question in the House of Commons, the UK Secretary of State for Foreign and Commonwealth Affairs stated:
In 1930, the Under-Secretary of State for Foreign Affairs … in reply to a Parliamentary Question on the scope of the [1925 Geneva Gas] Protocol said:
“Smoke screens are not considered as poisonous and do not, therefore, come within the terms of the Geneva Gas Protocol. Tear gases and shells producing poisonous fumes are, however, prohibited under the Protocol”
That is still the Government’s position. However, modern technology has developed CS smoke which, unlike the tear gases available in 1930, is considered to be not significantly harmful to man in other than wholly exceptional circumstances; and we regard CS and other such gases accordingly as being outside the scope of the [1925 Geneva Gas Protocol]. CS is in fact less toxic than the screening smokes which the 1930 statement specifically excluded. 
United Kingdom, House of Commons, Reply by the Secretary of State for Foreign and Commonwealth Affairs, Hansard, 2 February 1970, Vol. 795, Written Answers, p. 18.
In 1992, in reply to the question in the House of Commons “What allowances have been made for the retention of disabling agents for riot control purposes under the terms of the [1993 Chemical Weapons Convention]?”, the UK Minister of State, Foreign and Commonwealth Office, stated:
Under the terms of the [1993 Chemical Weapons Convention], states parties will be entitled to use toxic chemicals for law enforcement, including domestic riot control purposes, provided that such chemicals are limited to those not listed in the schedules to the convention and which can produce rapidly in humans sensory irritation or disabling physical effects which disappear within a short time following termination of exposure. States parties will undertake not to use riot control agents as a method of warfare. 
United Kingdom, House of Commons, Reply by the Minister of State, Foreign and Commonwealth Office, Hansard, 7 December 1992, Vol. 215, Written Answers, cols. 459–460.
In 1994, in reply to a question in the House of Commons about the use of gas weapons by the police, the UK Parliamentary Under-Secretary of State for Home Affairs stated:
The Association of Chief Police Officers is considering the possible use of products containing the incapacitating inflammatory agent, oleoresin capsicum … The only chemical agent which police forces are currently permitted to use is CS irritant. The considerable research which has been undertaken into this agent was evaluated by the 1969–1971 inquiry into the medical and toxicological aspects of CS … Police forces are permitted to use CS in extreme public order incidents where the chief officer of police judges such action to be necessary because of risk of loss of life or serious injury or widespread destruction of property; or against armed besieged criminals or violently insane persons where a senior officer judges that not to use it would endanger lives. There are no current proposals to change arrangements relating to CS. 
United Kingdom, House of Commons, Reply by the Parliamentary Under-Secretary of State for Home Affairs, Hansard, 31 March 1994, Vol. 240, Written Answers, col. 946.
In 1996, the House of Lords addressed a question to the UK Government to the effect that:
How is the development and manufacture of chemical weapons for “domestic riot control purposes”, which are included as “Purposes Not Prohibited Under this Convention’” in Article (9) of the Chemical Weapons Convention, to be distinguished from the development and manufacture of chemical weapons for purposes prohibited under the convention, and who is to be responsible for making these distinctions, and whether international peacekeeping operations are included among the “Purposes Not Prohibited Under this Convention”. 
United Kingdom, House of Lords, Question addressed to the Government by Lord Kennet, Hansard, 18 June 1996, Vol. 573, Written Answers, cols. 23–24.
In a written answer to this question, the UK Minister of State, Foreign and Commonwealth Office, replied:
The Chemical Weapons Convention prohibits the development and manufacture of any chemical weapons. The term “chemical weapons” includes toxic chemicals except those intended for purposes not prohibited by the convention, including “domestic riot control purposes”. Provided that the types and quantities of chemicals used are consistent with the intended permitted purpose they are not prohibited under the convention. Each State Party is obliged to declare details of chemicals held for riot control purposes (commonly known as riot control agents). The convention establishes a verification mechanism to monitor States Parties’ compliance with their obligations. The provisions include inspections of declared sites and investigations into allegations that riot control agents have been used in warfare. Inspections and investigations will be carried out by the Organisation for the Prohibition of Chemical Weapons.
The [Chemical Weapons Convention] prohibits the use of toxic chemicals as a method of warfare in international peacekeeping operations. 
United Kingdom, House of Lords, Reply by Minister of State, Foreign and Commonwealth Office, Hansard, 18 June 1996, Vol. 573, Written Answers, col. 24.
In 1998, the UK Minister of State for the Armed Forces provided a public explanation of why, in written answers to two parliamentary questions, he had told one questioner that “CS irritant is the only riot control agent held by my Department”, having just informed the other questioner that “the Ministry of Defence currently holds stocks of CR gas … a riot control agent designed to cause temporary irritation”. His explanation was that because the physiological effects of CR are among those which the 1993 Chemical Weapons Convention uses to define a “riot control agent” – because CR, in the words of Article II(7) 1993 Chemical Weapons Convention, “can produce rapidly in humans sensory irritation or disabling physical effects which disappear within a short time following termination of exposure” – CR can properly be described as a “riot control agent”, even though it is in fact held by the UK Defence Ministry for a purpose other than riot control, namely “maintaining an effective terrorism response capability”. 
United Kingdom, Letters dated 25 March 1998 from the Minister of State for the Armed Forces addressed to Messrs Harry Cohen and Ken Livingstone, with copies placed in the House of Commons Library.
In 1998, in reply to a question in the House of Lords, the UK Parliamentary Under-Secretary of State for Foreign and Commonwealth Affairs stated that the government had recently approved the export to the Netherlands of 2,500 rounds of CS gas and shotgun ammunition for use in riot control by the Dutch contingent to the UN forces in Bosnia and Herzegovina. 
United Kingdom, House of Lords, Reply to a question by the Parliamentary Under-Secretary of State for Foreign and Commonwealth Affairs, Hansard, 12 January 1998, Vol. 584, Written Answers, cols. 122–123.
In 2003, in a written reply to a question in the House of Commons, the UK Parliamentary Under-Secretary of State, Foreign and Commonwealth Office, stated:
All States Parties to the Chemical Weapons Convention (CWC) have undertaken not to use any toxic chemical or its precursor, including riot control agents (RCAs), as a method of warfare. This applies in any armed conflict. RCAs are defined in the CWC as any chemical not listed in a Schedule which can produce rapidly in humans sensory irritation or disabling physical effects which disappear within a short time following termination of exposure. (A chemical listed in a Schedule is one identified for the application of verification measures under the CWC.) 
United Kingdom, House of Commons, Written answer by the Parliamentary Under-Secretary of State, Foreign and Commonwealth Office, Hansard, 25 February 2003, Vol. 400, Written Answers, cols. 421W–422W.