24 SAADI v. THE UNITED KINGDOM JUDGMENT grant of authorisation to enter, the Court emphasises that such detention must be compatible with the overall purpose of Article 5, which is to safeguard the right to liberty and ensure that no-one should be dispossessed of his or her liberty in an arbitrary fashion. The Court must now consider what is meant by “freedom from arbitrariness” in the context of the first limb of Article 5 § 1(f) and whether, in all the circumstances, the applicant's detention was compatible with that provision. b) The notion of arbitrary detention in the context of Article 5 67. It is well established in the Court's case-law under the subparagraphs of Article 5 § 1 that any deprivation of liberty must, in addition to falling within one of the exceptions set out in sub-paragraphs (a)-(f), be “lawful”. Where the “lawfulness” of detention is in issue, including the question whether “a procedure prescribed by law” has been followed, the Convention refers essentially to national law and lays down the obligation to conform to the substantive and procedural rules of national law. Compliance with national law is not, however, sufficient: Article 5 § 1 requires in addition that any deprivation of liberty should be in keeping with the purpose of protecting the individual from arbitrariness (see, among many other authorities, Winterwerp, cited above § 37; Amuur, cited above, § 50; Chahal, cited above, § 118, and Witold Litwa, cited above, § 78). It is a fundamental principle that no detention which is arbitrary can be compatible with Article 5 § 1 and the notion of “arbitrariness” in Article 5 § 1 extends beyond lack of conformity with national law, so that a deprivation of liberty may be lawful in terms of domestic law but still arbitrary and thus contrary to the Convention. 68. While the Court has not previously formulated a global definition as to what types of conduct on the part of the authorities might constitute “arbitrariness” for the purposes of Article 5 § 1, key principles have been developed on a case-by-case basis. It is moreover clear from the case-law that the notion of arbitrariness in the context of Article 5 varies to a certain extent depending on the type of detention involved (see further below). 69. One general principle established in the case-law is that detention will be “arbitrary” where, despite complying with the letter of national law, there has been an element of bad faith or deception on the part of the authorities (see, for example, Bozano v. France, judgment of 18 December 1986, Series A no. 111; Čonka v. Belgium, no. 51564/99, ECHR 2002I). The condition that there be no arbitrariness further demands that both the order to detain and the execution of the detention must genuinely conform with the purpose of the restrictions permitted by the relevant sub-paragraph of Article 5 § 1 (Winterwerp, cited above, § 39; Bouamar v. Belgium, judgment of 29 February 1988, Series A no. 129, § 50; O'Hara v. the United Kingdom, no. 37555/97, § 34, ECHR 2001-X). There must in addition be