Britain's security relationship with its European allies was being galvanized by common problems such as dealing with terrorists and brides returning to Europe after the collapse of Daesh terror organizaton's "caliphate" in Syria and Iraq.
"We are very concerned about this because all experience tells us that once someone has put themselves in that sort of position they are likely to have acquired the skills and connections that make them potentially very dangerous," he said.
"The reality is that so far, it has been a completely manageable problem," he added. "I can't predict accurately what will happen in future, but it's a very complex environment."
Daesh terrorists have morphed and are proving "adept at inspiring at attacks rather than directing them", he said.
"Al Qaeda, which has always been in a rivalry, and almost zero sum relationship with Daesh, has, I think, undergone a certain resurgence as a result of the degradation of Daesh," he added. "It is definitely not down and out."
Turning to Russia, Younger said he believed it was "intent on breaking up the links and alliances that exist" between Western states and that he was determined to attach a cost to any such efforts.
Asked whether former Russian spy Sergei Skripal and his daughter Yulia remained under threat after an assassination attempt that British authorities blame on Russia, Younger said:
"I think there is a standing threat from the GRU (military intelligence agency) and other Russian intelligence services and that very little is off limits."
