There is a book on this very subject (although heavily covering U.S. flights) that is a superb read. It is "By any means necessary". Sadly I do not have it to hand at the moment, so cannot list the ISBN number, but am sure is is on amazon or similar.
This book covers RAF flights, and how some crews realised their flight plan had been given to the soviets in advance!, with the tale tale sign being that anti aircraft guns were actually opening fire ahead of the aircraft on its planned route.
It also covers U.S. SR71 flights, and their associated drones (including at least one which landed in foreign territory).
Sadly it also documents the fate of several crews who were killed, or captured, and their subsequent fate.
Well worth a read, if not always easy reading.