In 1934, the KGB, The Soviet security intelligence agency, recruited three Cambridge University Students: Guy Burgess, Donald Maclean and Harold "Kim" Philby. Three years later, in 1937, two more were recruited: Anthony Blunt and John Cairncross; thus, creating the Cambridge Five.
Note: add to research for the Bond book. Separate bios for Burgess, Maclean and Philby?
  Through their activities the Cambridge Five had manage to interfere with virtually every intelligence and counter-intelligence operations by western security agencies. The information passed on to the Soviets was of incredible value. The most of important of which were nuclear weapons secrets, which some experts claim, helped the Soviet Union develop the atomic bomb more than two years sooner than it would have. In addition, not a single member of the Cambridge Five was ever prosecuted.
Note: legal procedures at that time in England? Standards of proof? Extradition?