Reuters/Stuttgart, Germany

At the moment of her arrest in 2011, Heidrun Anschlag was, in true spy thriller fashion, receiving a coded radio transmission from Moscow, the court said.

“Through their excellent training and carefully crafted cover stories ... the defendants posed a significant, abstract danger to Germany,” said the judges, sentencing Heidrun Anschlag and her husband Andreas – not their real names – to 5-1/2 and 6-1/2 years’ prison respectively.

The pair, now in their 50s, entered Germany in 1988 and 1990, posing as Austrian citizens from South America.

While their cover has been broken, investigators have to this day failed to uncover their true identities.

From their home in the university town of Marburg, they passed on political and military secrets from the EU and Nato obtained from a contact in the Dutch foreign ministry’s visa section, and sought out recruits.

From 2008, their main task became managing this contact, who was paid at least 72,200 euros ($94,100).

Described by Moscow as a “valuable source in need of particular protection”, the Dutch man was arrested in March 2012 and jailed for 12 years.

German media have said Andreas Anschlag was an engineer in the automobile assembly industry – a sector chosen because of the possibilities it offered for industrial espionage, although there was no proof he had been successful in this.

His wife was a housewife and they had one daughter, the reports have said.

Although the documents passed to Russia were classified at the lowest grade of confidentiality, and no damage to German, Dutch, Nato or EU interests was established, the judges said the betrayal was “considerable” and the couple had damaged faith in the ability of Germany and its partners to protect information.

The couple could have been jailed for up to 10 years, but their lawyer Horst-Dieter Poetschke nevertheless criticised the sentences.

“Spying happens everywhere and it’s not right that one person is sentenced for belonging to a particular country ... also, spying has its advantages because, if you realise what the enemy is planning, you can adjust to it, not just in bad terms but also in good terms, and act in the interest of peace.”