A truly excellent episode of Archive on 4 examining to what extent spy stories are likely to be based on fact. There are a number of authors featured, starting from the earliest days of the genre including W. Somerset Maugham (Ashenden: Or the British Agent), Erskine Childers (The Riddle of the Sands), John Buchan (The Thirty-Nine Steps), John Le Carré (The Spy Who Came in from the Cold) and Ian Fleming (James Bond).
A big omission: Len Deighton.
If you like the genre, this comes highly recommended.
• BBC Radio 4 (Archive on 4): Great Spy Books – Fact or Fiction?