22 SAADI v. THE UNITED KINGDOM JUDGMENT if the Grand Chamber were to uphold the Chamber's view and give States complete freedom to deprive all asylum seekers of their liberty whilst their claims were being processed, without any requirement to show that the detention was necessary for the purpose specified in Article 5 § 1(f), namely to prevent the making of an unauthorised entry. 4. The Court's assessment a) The meaning of the phrase “... to prevent his effecting an unauthorised entry into the country” 61. In the present case the Court is called upon for the first time to interpret the meaning of the words in the first limb of Article 5 § 1(f), “... lawful ... detention of a person to prevent his effecting an unauthorised entry into the country ...” (in French: “la détention [régulière] d'une personne pour l'empêcher de pénétrer irrégulièrement dans le territoire”). In ascertaining the Convention meaning of this phrase, it will, as always, be guided by Articles 31 to 33 of the Vienna Convention on the Law of Treaties (paragraphs 26-28 above, and see, for example, Golder v. the United Kingdom, judgment of 21 February 1975, Series A no. 18, § 29; Johnston and Others v. Ireland, judgment of 18 December 1986, Series A no. 112, § 51 et seq.; Lithgow and Others v. the United Kingdom, judgment of 8 July 1986, Series A no. 102, §§ 114 and 17; Witold Litwa v. Poland, cited above, §§ 57-59). 62. Under the Vienna Convention on the Law of Treaties, the Court is required to ascertain the ordinary meaning to be given to the words in their context and in the light of the object and purpose of the provision from which they are drawn (see the Golder judgment, § 29; the Johnston judgment, § 51; and Article 31 § 1 of the Vienna Convention). The Court must have regard to the fact that the context of the provision is a treaty for the effective protection of individual human rights and that the Convention must be read as a whole, and interpreted in such a way as to promote internal consistency and harmony between its various provisions (Stec and Others v. the United Kingdom (dec.) [GC], nos. 65731/01 and 65900/01, § 48, ECHR 2005-X). The Court must also take into account any relevant rules and principles of international law applicable in relations between the Contracting Parties (see Al-Adsani v. the United Kingdom, cited above, § 55; Bosphorus Hava Yollari Turizm Ve Ticaret Anonim Sirketi v. Ireland [GC], no. 45036/98, § 150, ECHR 2005-III; and Article 31 § 3(c) of the Vienna Convention). Recourse may also be had to supplementary means of interpretation, including the preparatory works to the Convention, either to confirm a meaning determined in accordance with the above steps, or to establish the meaning where it would otherwise be ambiguous, obscure or manifestly absurd or unreasonable (Article 32 of the Vienna Convention).