A. AND OTHERS v. THE UNITED KINGDOM JUDGMENT 67 detained as persons “against whom action is being taken with a view to deportation or extradition”. 164. Article 5 § 1 (f) does not demand that detention be reasonably considered necessary, for example to prevent the individual from committing an offence or fleeing. Any deprivation of liberty under the second limb of Article 5 § 1 (f) will be justified, however, only for as long as deportation or extradition proceedings are in progress. If such proceedings are not prosecuted with due diligence, the detention will cease to be permissible under Article 5 § 1 (f) (see Chahal, cited above, § 113). The deprivation of liberty must also 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. 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 (see Saadi, cited above, § 67). To avoid being branded as arbitrary, detention under Article 5 § 1 (f) must be carried out in good faith; it must be closely connected to the ground of detention relied on by the Government; the place and conditions of detention should be appropriate; and the length of the detention should not exceed that reasonably required for the purpose pursued (see, mutatis mutandis, Saadi, cited above, § 74). 165. The first, third, and sixth applicants were taken into detention under the 2001 Act on 19 December 2001; the seventh applicant was detained on 9 February 2002; the eighth applicant on 23 October 2002; the ninth applicant on 22 April 2002; the tenth applicant on 14 January 2003; and the eleventh applicant on 2 October 2003. None of these applicants was released until 10-11 March 2005. The fifth applicant was detained between 19 December 2001 and 22 April 2004, when he was released on bail subject to stringent conditions. The second and fourth applicants were also detained on 19 December 2001 but the second applicant was released on 22 December 2001, following his decision to return to Morocco, and the fourth applicant was released on 13 March 2002, following his decision to go to France. The applicants were held throughout in high security conditions at either Belmarsh or Woodhill Prisons or Broadmoor Secure Mental Hospital. It cannot, therefore, be disputed that they were deprived of their liberty within the meaning of Article 5 § 1 (see Engel and Others v. the Netherlands, 8 June 1976, Series A no. 22).