Not totally on topic, but not totally off-topic. At the moment I am reading a couple of history books by Ben McIntyre about WW2 and cold war spies. During WW2 Germany had almost no spy presence in Great Britain, and when they sent spies over they were either captured pretty quickly because they were so ill-prepared and inept, or upon arrival in the country they turned themselves in and many became double agents working against Germany.
However on the other hand, the Russians had an extensive and highly effective UK based spy network throughout WW2 and into the cold war era, and their spies included high ranking staff in MI5 / MI6 and other parts of the establishment, and they went undetected for years on end. They recruited many through the public school old-boys network.
His books are well worth a read if you are at all interested in that kind of stuff.