AUAD v. BULGARIA JUDGMENT 45 the applicant spent exactly eighteen months in custody, the maximum period allowed by law. Contrary to what has been suggested by the Government, compliance with that time-limit, which is in any event exceptional (see paragraphs 47, 48, 50 and 51 above), cannot automatically be regarded as bringing the applicant’s detention into line with Article 5 § 1 (f) of the Convention. As noted above, the relevant test under that provision is rather whether the deportation proceedings have been prosecuted with due diligence, which can only be established on the basis of the particular facts of the case. 132. Here, it appears that the only steps taken by the authorities during the eighteen months in issue were to write three times to the Lebanese embassy in Sofia with requests for the issuing of a travel document for the applicant (see paragraph 26 above). While the Bulgarian authorities could not compel the issuing of such a document, there is no indication that they pursued the matter vigorously or endeavoured entering into negotiations with the Lebanese authorities with a view to expediting its delivery (see Raza, cited above, § 73; Tabesh v .Greece, no. 8256/07, § 56, 26 November 2009; and Louled Massoud v. Malta, no. 24340/08, § 66, 27 July 2010). Moreover, apart from their own statements for the purposes of the proceedings before the Court, the Government have not provided evidence of any effort having been made to secure the applicant’s admission to a third country. The authorities can thus hardly be regarded as having taken active and diligent steps with a view to deporting him. It is true that the applicant’s detention was subject to periodic judicial review, which provided an important safeguard (see Dolinskiy v. Estonia (dec.), no. 14160/08, 2 February 2010). However, that cannot be regarded as decisive. The last such review took place on 7 December 2010 (see paragraph 26 above), whereas the Court has not been informed whether any steps were taken with a view to removing the applicant from that time until his release more than five months later, on 19 May 2011 (see, mutatis mutandis, Mikolenko, cited above, § 64 in fine). 133. The assessment of those points is further frustrated by the fact that neither the expulsion order nor any other binding legal act specified the destination country, as this was not required under domestic law (see paragraphs 39 and 40 above). The Court considers that this may be seen as problematic with regard to the requirement of legal certainty inherent in all Convention provisions. Where deprivation of liberty is concerned, legal certainty must be strictly complied with in respect of each and every element relevant to the justification of the detention under domestic and Convention law. In cases of aliens detained with a view to deportation, lack of clarity as to the destination country could hamper effective control of the authorities’ diligence in handling the deportation. 134. It is true the applicant did not spend such a long time in detention as the applicants in some other cases, such as Chahal (cited above).