British counterintelligence limited German clandestine operations

Could successful German clandestine operations from the world wars still be secret or lost because their documentation disappeared?

Possibly, but British counterintelligence made German operations in Britain difficult, especially when they depended on inserting foreign agents.

Successful German clandestine operations may remain secret or have lost their documentation. British counterintelligence nevertheless created serious difficulties for German agents in both world wars. Foreign agents entering Britain were often easier to detect than people recruited within British society. The later Soviet penetrations associated with Cambridge illustrate that distinction: insiders could move through familiar institutions and social networks more easily.