The Directive requires telecoms companies to store user data – such as calling telephone number and the name and address of service users – for up to two years, and to make it available to law enforcement authorities on request. It was intended to be an anti-terrorism measure aimed at protecting the public, as well as a way for law enforcement authorities to combat other crimes.

But, as described in a press release describing the outcome, the ECJ ruled that the directive is invalid on the grounds that it clashes with two fundamental rights under the Charter of Fundamental Rights of the EU: the fundamental right to respect for private life and the fundamental right to the protection of personal data.

The ECJ’s review of the directive came about following a request by the Irish and Austrian courts to examine the validity of the law.

In a statement on the judgement, the European Commission’s commissioner for Home Affairs, Cecilia Malmström, said: “The judgment of the Court brings clarity and confirms the critical conclusions in terms of proportionality of the Commission’s evaluation report of 2011 on the implementation of the data retention directive.

“The European Commission will now carefully asses the verdict and its impacts. The Commission will take its work forward in light of progress made in relation to the revision of the e-Privacy directive and taking into account the negotiations on the data protection framework.”