Britain’s security services will be conducting a major review of intelligence that may have been compromised after a former German spy chief was arrested on suspicion of espionage, experts have told The i Paper.

August Hanning, 80, who was head of Germany’s Federal Intelligence Service (BND) from 1998 to 2005, is accused of illegally collecting thousands of classified documents and using them in analysis for a foreign spy service.

German newspaper has said the information taken includes “highly sensitive situation assessments, classified material from foreign partner agencies” as well as papers on Iran’s nuclear programme and the Russian military.

Professor Anthony Glees, an expert on intelligence and UK-German relations, claimed the alleged breach could be Europe’s most serious since British double agent Kim Philby was unmasked as a Soviet spy at the height of the Cold War in 1963.

“It is totally jaw-dropping and the repercussions could hardly be more serious,” he told The i Paper. “It is as if Blaise Metreweli [the current MI6 chief] were arrested.”

Matthew Dunn, a former MI6 officer, told The i Paper that intelligence relating to state-sponsored terrorism, espionage or political destabilisation could now be compromised.

However he did point out that intelligence shared with allied countries is often sanitised to safeguard against leaks.

As Europe’s biggest intelligence service, the BND is a routine recipient of highly classified information from agencies including MI6 and the CIA.

Five years after his tenure as head of the BND ended, Hanning ⁠allegedly agreed with a former office manager to receive ‌confidential intelligence information in exchange for payment, according to prosecutors.

Hanning’s ex-chief of staff, Manfred D, is alleged to have supplied him with nearly 2,000 BND documents. Hanning allegedly used these to inform his private consultancy business. 

Manfred was also chief of staff for Hanning’s successors between 2012 and 2026 and is alleged to have provided him with information until at least mid-2022.

Russia currently ‘not part of investigation’

According to Deutsche Welle, Hanning also allegedly maintained close contact for years with an employee of a foreign intelligence service. 

Officials familiar with the investigation have told the that Russia was not currently part of their investigation. 

Hanning is said to have prepared an analysis for the Azerbaijani intelligence services, the German newspaper has reported.

Glees said other states that could be implicated include “the usual suspects”, citing China, Iran and North Korea.

Since it was founded in 1956, the BND had become almost an “external arm” of the CIA, he said, with the US intelligence agency working in close co-operation alongside its German counterparts.

“The CIA will be absolutely beside themselves, as will MI6,” said the professor.

The BND had largely provided British intelligence with information about Islamist terrorism as well as Russia, he added.

If Hanning were working alongside a foreign intelligence service, any information the BND may have received about that country “may well have been tainted”, said Glees.

That, in turn, could mean any decisions the UK took about that particular country could also have been based on false information, he added.

“The opportunity for disinformation is absolutely massive,” he said, with the potential damage caused “enormous”.

But Dunn said information shared between intelligence agencies is likely “sanitised… precisely because of these possibilities that the end recipient could be a bit leaky. Life can be lost so the biggest jeopardy is at stake here.”

For instance, he said the identities of serving intelligence and their agents are protected.

Any intelligence about potential enemy spies operating in the UK would also only be shared with Germany if required, such as if there was a link to a handler in Germany, Dunn said.

He added that British intelligence agencies “will be right now, no doubt, doing a full security overview of all intelligence shared during any period that’s deemed vulnerable because of leaks within Germany”.

“In terms of feeding knowledge of our enemies back to the enemy itself, yes, that is an area of vulnerability,” he said. “The biggest fear always, always, always in intelligence is the dreaded double agent scenario.”

Sir Richard Dearlove, the former head of the MI6, warned in 2024 that he was highly selective about what intelligence he shared with the BND over fears it would leak to Russia.

“There was certain highly sensitive stuff we wouldn’t have given them in a month of Sundays,” he told .

However, in the interview, he mentioned Hanning as someone who did take security issues “seriously”. described Hanning as a “personal friend” of Dearlove.

Hanning had even warned himself about the risk of Russia’s eavesdropping on sensitive calls.