Germany has sought explanations from British ministers over GCHQ’s Project Tempora surveillance operation, which reportedly monitored global phone and Internet traffic on a mass scale.

German Justice minister Sabine Leutheusser-Schnarrenberger has written to Justice Secretary Chris Grayling and Home Secretary Theresa May questioning the programme’s legal basis, according to Guardian.

She warned the UK ministers that she would raise the issue at the July meeting of EU justice and home affairs ministers in Brussels.

The move expresses Germany citizens’ growing anger over GCHQ’s surveillance activities along with its American counterpart, the National Security Agency (NSA).

Leutheusser-Schnarrenberger, in her letter, seeks clarification of the legal basis for the operation and whether it was authorised by any judicial authority.

"I feel that these issues must be raised in a European Union context at minster’s level and should be discussed in the context of ongoing discussions on the EU data protection regulation," Leutheusser-Schnarrenberger wrote.

It was confirmed by the Ministry of Justice that it had received Leutheusser-Schnarrenberger’s letter. The ministry said it would respond ‘in due course’.

A Home Office spokesman said: "We do not routinely comment on private correspondence."

Konstantin von Notz, the interior affairs spokesman of the opposition Green party, was quoted by Guardian as telling Deutsche Welle: "What’s been going on here is against international law and must be stopped immediately."