The BND agency's surveillance violates “the fundamental right to privacy of telecommunications” and freedom of the press, judges at the Constitutional Court in Karlsruhe said in their verdict.

But given the “great importance” of foreign surveillance to German security, the court gave the BND until the end of 2021 to change its practices to comply with the law.

The ruling marked the first time the  Constitutional Court clearly stated that the BND must respect fundamental rights accorded by the constitution even when operating abroad.

German intelligence services are already not allowed to monitor the internet traffic of Germans in such a vast way.

The case was brought by journalists and civil society groups who were outraged after the BND was granted sweeping new powers to carry out “strategic telecommunications surveillance” under amended legislation in 2016.

This allowed the BND to tap into internet traffic from non-Germans abroad, often through monitoring the use of keywords, phone numbers or email addresses, and to share this information with other secret services.

One of the plaintiffs, Reporters Without Borders, argued that this allowed the agency to spy on journalists “almost without restrictions”.

“The big victory is that German authorities cannot get out of their constitutional obligations by going abroad and working there,” said Nora Markard from the GFF Society for Civil Rights, another of the co-plaintiffs.