SAADI v. THE UNITED KINGDOM JUDGMENT 25 some relationship between the ground of permitted deprivation of liberty relied on and the place and conditions of detention (see the abovementioned Bouamar judgment, § 50; Aerts v. Belgium, judgment of 30 July 1998, Reports 1998-V, § 46; Enhorn v. Sweden, no. 56529/00, § 42, ECHR 2005-I). 70. The notion of arbitrariness in the contexts of sub-paragraphs (b), (d) and (e) also includes an assessment whether detention was necessary to achieve the stated aim. The detention of an individual is such a serious measure that it is justified only as a last resort where other, less severe measures have been considered and found to be insufficient to safeguard the individual or public interest which might require that the person concerned be detained (see Witold Litwa, cited above, § 78; Hilda Hafsteinsdóttir v. Iceland, no. 40905/98, § 51, 8 June 2004; Enhorn v. Sweden, cited above, § 44). The principle of proportionality further dictates that where detention is to secure the fulfilment of an obligation provided by law, a balance must be struck between the importance in a democratic society of securing the immediate fulfilment of the obligation in question, and the importance of the right to liberty (see Vasileva v. Denmark, no. 52792/99, § 37, 25 September 2003). The duration of the detention is a relevant factor in striking such a balance (ibid., and see also McVeigh and Others v. the United Kingdom, applications nos. 8022/77, 8025/77, 8027/77, Commission decision of 18 March 1981, DR 25, pp. 37-38 and 42). 71. The Court applies a different approach towards the principle that there should be no arbitrariness in cases of detention under Article 5 § 1(a), where, in the absence of bad faith or one of the other grounds set out in paragraph 69 above, as long as the detention follows and has a sufficient causal connection with a lawful conviction, the decision to impose a sentence of detention and the length of that sentence are matters for the national authorities rather than for the Court under Article 5 § 1 (see T. v. the United Kingdom [GC], no. 24724/94, § 103, ECHR 2000-I ; and also Stafford v. the United Kingdom [GC], no. 46295/99, § 64, ECHR 2002-IV). 72. Similarly, where a person has been detained under Article 5 § 1(f), the Grand Chamber, interpreting the second limb of this sub-paragraph, held that, as long as a person was being detained “with a view to deportation”, that is, as long as “action [was] being taken with a view to deportation”, there was no requirement that the detention be reasonably considered necessary, for example to prevent the person concerned from committing an offence or fleeing (Chahal, cited above, § 112). The Grand Chamber further held in Chahal that the principle of proportionality applied to detention under Article 5 § 1(f) only to the extent that the detention should not continue for an unreasonable length of time; thus, it held (§ 113) that “any deprivation of liberty under Article 5 § 1(f) will be justified only for as long as deportation proceedings are in progress. If such proceedings are not prosecuted with due diligence, the detention will cease to be permissible ...”