MI6 investigates whether British secrets were compromised after arrest of former German spy chief

British intelligence agencies are investigating whether classified information or human sources may have been compromised following the arrest of a former head of Germany's foreign intelligence service on suspicion of espionage and treason.

August Hanning, who led Germany's Federal Intelligence Service, the BND, from 1998 to 2005, was arrested at his home near Münster earlier this month. A former aide, identified only as Manfred D, was also arrested, accused of passing Mr Hanning around 2,000 classified documents in exchange for payment over a sixteen-year period.

German federal prosecutors allege that Mr Hanning used some of that classified intelligence to draft an analysis for an officer of a foreign intelligence service, and that he maintained contact with another unnamed foreign spying agency. Prosecutors have not disclosed which countries were involved.

Why Britain is concerned

Manfred D served as chief of staff to successive heads of the BND between 2012 and earlier this year, giving him access to highly sensitive material, including intelligence shared by partner agencies abroad. German security sources say some of that information came from allied services, raising fears in London and Washington that British and American secrets, and potentially the identities of human sources operating in the field, could have been exposed.

MI6 and GCHQ are understood to be carrying out a systematic internal review of all sensitive material shared with German counterparts during the period covered by the allegations, with the primary focus on protecting any agents or informants who may have been put at risk. Similar audits are expected to be carried out by other Western intelligence agencies that routinely share information with Germany.

Sources within the Western intelligence community have described the case as one of the most serious breaches to affect an allied agency since the end of the Cold War, with the potential to do lasting damage to trust between European intelligence services at a time when cooperation against Russian activity is seen as critical.

A historically cautious relationship

Former British intelligence chiefs have said that, despite his seniority, Mr Hanning was never regarded as being as close to UK agencies as counterparts in France or the United States. Sir Francis Richards, who led GCHQ from 1998 to 2003 while Mr Hanning ran the BND, said their relationship had not been "terribly close", citing long-standing British unease about the complexities of German domestic politics and the BND's historically more nuanced relationship with Russia.

Other former senior officials have gone further, suggesting that British agencies were wary of sharing their most sensitive material with Germany even before the current allegations emerged, precisely because of long-held concerns about the security of German intelligence structures.

The case against Hanning

German prosecutors say Manfred D used his privileged access within the BND to gather classified documents, which he then passed to Mr Hanning for money. On at least one occasion, prosecutors allege, Mr Hanning used that intelligence to produce an analysis for an officer of a foreign agency, though it remains unclear whether the material ultimately reached its intended recipient.

Mr Hanning, now 80 years old, has worked as a private security consultant since leaving government service two decades ago. He is due to appear in court, along with Manfred D, as the German investigation proceeds. Neither has publicly responded in detail to the allegations.

The wider picture

The case lands amid a broader period of heightened concern about espionage threats facing the UK and its allies. Earlier this week, a serving member of the Royal Navy was charged under the National Security Act with offences relating to the handling of protected information allegedly intended to benefit a foreign power, in a case that police say is unconnected to the Hanning investigation.

MI5 has also recently issued a rare public warning to British universities about a Chinese-linked research institute it says exists primarily to fund work that improves Beijing's intelligence-gathering capabilities, after identifying more than 100 UK-linked academics who had contributed to projects it funded.

Taken together, officials say the cases illustrate the scale and variety of the espionage challenge currently facing British intelligence agencies, spanning everything from state-sponsored infiltration of academic institutions to the potential compromise of decades-old intelligence-sharing arrangements with a close European ally.

What happens next

British agencies are not expected to comment publicly on the detail of their review, in keeping with long-standing practice around operational security matters. But the scale of the exposure will not be fully understood until German prosecutors set out more detail of exactly what information passed through Mr Hanning and Manfred D, and over what period.

For now, the priority for MI6 and GCHQ is understood to be identifying and, where necessary, moving any sources whose safety could have been compromised, a process that officials say could take months to complete even as the German legal case against the two men continues to unfold.