18 SAADI v. THE UNITED KINGDOM JUDGMENT the sub-paragraph, so that a person who had been living within the community could be detained in conjunction with a deportation even though this was not necessary to prevent his absconding, but a person who had newly arrived could be detained in conjunction with his arrival only where this was necessary to prevent his absconding. 50. The Government further denied that the applicant's detention had been unlawful or arbitrary. It was clear, as the national courts at three instances unanimously confirmed, that the detention had complied with the substantive and procedural rules of national law (see paragraphs 16-18 above). The detention was not arbitrary, since, as the Chamber had held, it had been a genuine part of the process to determine whether the individual should be granted immigration clearance and/or asylum, and its duration had been limited to that which was reasonably necessary for that purpose. To argue, as did the applicant, that the detention had been arbitrary because it might have been possible to achieve the same purpose by use of an “accommodation centre”, with similar conditions of residence but no confinement, was misplaced, since it involved seeking to reintroduce the “necessity” requirement through the requirement of lack of arbitrariness. In any event, the House of Lords had found that, given the tight schedule of interviews, any arrangement short of detention would not have been as effective (see paragraph 18 above). b) The applicant 51. The applicant submitted that the Convention had to be interpreted in accordance with Articles 31-33 of the Vienna Convention on the Law of Treaties (see paragraphs 26-28 above). He did not dispute the State's sovereign right to control the entry and presence of aliens on its territory, but emphasised that this right had to be exercised consistently with the State's international obligations, in particular those contained in the Convention, including Article 5. The purpose defined by Article 5 § 1(f) first limb was to prevent unlawful immigration, that is, entry and residence in a country by the circumvention of immigration control. There had to be a direct and precise causal relationship between the detention and the risk of unauthorised entry. This purpose was underlined by the words “his effecting”, indicating that the focus was upon whether the particular individual, if not detained, would otherwise effect an entry that was unauthorised. It was clear from the facts of the applicant's case that, if he had not been detained, he would have been lawfully present in the United Kingdom with “temporary admission”, an “authorised” status in fact and law (see, inter alia, the House of Lords' judgment in Szoma, paragraph 21 above). The interpretation he advanced would allow for initial detention for the purposes of verification and assessment of the individual risk of unauthorised entry; such procedure formed part of the ordinary process of immigration control, and was plainly detention for the purpose of