Member States shall adopt measures to ensure that data retained in accordance with this Directive are provided only to the competent national authorities in specific cases and in accordance with national law. The procedures to be followed and the conditions to be fulfilled in order to gain access to retained data in accordance with necessity and proportionality requirements shall be defined by each Member State in its national law, subject to the relevant provisions of European Union law or public international law, and in particular the ECHR as interpreted by the European Court of Human Rights.