33 McCANN AND OTHERS v. THE UNITED KINGDOM JUDGMENT described in the following terms in the report of the Royal Commission appointed to consider the law relating to indictable offences ([1879] 36 House of Lords Papers 117, at p. 167): "We take one great principle of the common law to be, that though it sanctions the defence of a man’s person, liberty and property against illegal violence, and permits the use of force to prevent crimes to preserve the public peace and to bring offenders to justice, yet all this is subject to the restriction that the force used is necessary; that is, that the mischief sought to be prevented could not be prevented by less violent means; and that the mischief done by or which might reasonably be anticipated from the force used is not disproportionate to the injury or mischief, which it is intended to prevent." Lord Justice McGonigal in Attorney General for Northern Ireland’s Reference ([1976] Northern Ireland Law Reports 169 (Court of Appeal)) stated his understanding of this approach as follows (at p. 187): "... it appears to me that, when one is considering whether force used in any particular circumstances was reasonable, the test of reasonableness should be determined in the manner set out in that paragraph. It raises two questions: (a) Could the mischief sought to be prevented have been prevented by less violent means? (b) Was the mischief done or which could reasonably be anticipated from the force used disproportionate to the injury or mischief which it was intended to prevent? These are questions to be determined objectively but based on the actions of reasonable men who act in the circumstances and in the light of the beliefs which the accused honestly believed existed and held. Force is not reasonable if (a) greater than that necessary, or (b) if the injury it causes is disproportionately greater than the evil to be prevented." 136. The document annexed to the operational order of the Commissioner of Police entitled "Firearms - rules of engagement" provided in so far as relevant: "General rules 1. Do not use more force than necessary to achieve your objective. 2. If you use firearms you should do so with care for the safety of persons in the vicinity. 3. Warning before firing (a) A warning should, if practicable, be given before opening fire. It should be as loud as possible and must include an order to stop attacking and a statement that fire will be opened if the orders are not obeyed.