This was more or less a plot point in Slow Horses. Solid show.
I believe it also served as some inspiration for the agents in The Division, basically when shit goes very sideways, agents hidden amongst the public spring into action and respond to whatever is going on.
“Operation Gladio was the codename for clandestine “stay-behind” operations of armed resistance that were organized by the Western Union (WU) (founded in 1948), and subsequently by NATO (formed in 1949) and by the CIA (established in 1947),[1][2] in collaboration with several European intelligence agencies during the Cold War.[3] Although Gladio specifically refers to the Italian branch of the NATO stay-behind organizations, Operation Gladio is used as an informal name for all of them. Stay-behind operations were prepared in many NATO member countries, and in some neutral countries.[4]”
