DRAGOJEVIĆ v. CROATIA JUDGMENT 35 a violation of another Convention right is concerned, the nature of the violation found (see Allan v. the United Kingdom, no. 48539/99, § 42, ECHR 2002-IX). 129. In determining whether the proceedings as a whole were fair, regard must also be had to whether the rights of the defence were respected. It must be examined in particular whether the applicant was given the opportunity of challenging the authenticity of the evidence and of opposing its use. In addition, the quality of the evidence must be taken into consideration, including whether the circumstances in which it was obtained cast doubt on its reliability or accuracy. While no problem of fairness necessarily arises where the evidence obtained was unsupported by other material, it may be noted that where the evidence is very strong and there is no risk of its being unreliable, the need for supporting evidence is correspondingly weaker (see, amongst many others, Bykov, cited above, § 90). 130. As regards, in particular, the examination of the nature of the Convention violation found, the Court observes that in several cases it has found the use of covert listening devices to be in breach of Article 8 since such interference was not “in accordance with the law”. Nonetheless, the admission in evidence of information obtained thereby did not in the circumstances of a particular case conflict with the requirements of fairness guaranteed by Article 6 § 1 (see Khan, cited above, §§ 25-28; P.G. and J.H. v. the United Kingdom, no. 44787/98, §§ 37-38, ECHR 2001-IX; and Bykov, cited above, §§ 94-105). (ii) Application of these principles to the present case 131. The Court notes at the outset that the applicant did not put forward any argument disputing the reliability of the information obtained by secret surveillance measures but limited his objection exclusively to the formal use of such information as evidence during the proceedings (compare Khan, cited above, § 38; P.G. and J.H., cited above, § 79; and Bykov, cited above, § 95). 132. He also had an effective opportunity to challenge the authenticity of the evidence and oppose its use and used that opportunity during the proceedings before the first-instance court (see paragraphs 35 and 42 above), and in his appeal (see paragraph 47 above) and constitutional complaint (see paragraph 49 above). The domestic courts examined his arguments on the merits and provided reasons for their decisions (see paragraphs 46, 48 and 50 above). The fact that the applicant was unsuccessful at each step does not alter the fact that he had an effective opportunity to challenge the evidence and oppose its use (see Schenk, cited above, § 47, and Khan, cited above, § 38). 133. The Court further notes that the impugned evidence was not the only evidence on which the conviction was based (compare Schenk, cited