Article 4 of the Optional Protocol: 1. Each State Party shall allow visits, in accordance with the present Protocol, by the mechanisms referred to in articles 2 and 3 to any place under its jurisdiction and control where persons are or may be deprived of their liberty, either by virtue of an order given by a public authority or at its instigation or with its consent or acquiescence (hereinafter referred to as places of detention). These visits shall be undertaken with a view to strengthening, if necessary, the protection of these persons against torture and other cruel, inhuman or degrading treatment or punishment. 2. For the purpose of the present Protocol, deprivation of liberty means any form of detention or imprisonment or the placement of a person in a public or private custodial setting which that person is not permitted to leave at will by order of any judicial, administrative or other authority. The Subcommittee has interpreted the scope of article 4 of the Optional Protocol as follows: Article 4 contains two paragraphs that must be read together and that place within the scope of the Optional Protocol any public or private custodial setting under the jurisdiction and control of the State Party, in which persons may be deprived of their liberty and are not permitted to leave, either by an order given by any judicial, administrative or other authority or at its instigation or with its consent or acquiescence. The preventive approach underpinning the Optional Protocol means that as extensive an interpretation as possible should be made in order to maximize the preventive impact of the work of the National Preventive Mechanism. The Subcommittee therefore takes the view that any place in which persons are deprived of their liberty, in the sense of not being free to leave, or in which the Subcommittee considers that persons might be being deprived of their liberty, should fall within the scope of the Optional Protocol, if the deprivation of liberty relates to a situation in which the State either exercises, or might be expected to exercise, a regulatory function. In all situations, the National Preventive Mechanism should also be mindful of the principle of proportionality when determining its priorities and the focus of its work. (CAT/OP/C/57/4) II. Access to persons NPMs should have access to all persons, without the presence of the authorities, whose accounts they may consider necessary in undertaking their mandates. They should be able to decide for themselves which persons they should interview, including (i) persons deprived of their liberty from all areas and units, (ii) administrative and other staff of the visited institutions, and (iii) their visitors, such as members of civil society and others, including organizations working with persons at heightened risk (such as migrants, ethnic and cultural minorities, and persons with disabilities). They should also be able to decide when, where and how such persons are to be interviewed. III. Access to information NPMs should seek and be able to obtain prompt, regular and unhindered access to all information relating to persons deprived of their liberty during their visits, including registers, case records, personal files, incident registers, medical records and all other information necessary for pursuing their mandates, 22 I PREVENTING TORTURE: THE ROLE OF NATIONAL PREVENTIVE MECHANISMS – A PRACTICAL GUIDE