• Macfarlan, Captain Kenneth ‘Pinky’ 1
• Mackeson, G. P. 1
• Macmillan, Harold 1
• Magdeburg (cruiser) 1
• The Man Who Never Was (Montagu) 1
• Mask operation (Comintern) 1, 2g
• Masterman, John 1
• Matapan, Battle of 1, 2, 3
• Mediterranean (GGG network) 1, 2, 3
• Menzer, Fritz 1
• Menzies, Colonel Stewart 1, 2, 3, 4, 5, 6, 7
• message intercepts 1, 2, 3, 4, 5, 6
• Mexico, World War I 1, 2
• MI5
  • double agents 1, 2, 3
  • Twenty (XX) Committee (Double Cross) 1, 2, 3, 4
• MI6 see Secret Intelligence Service (SIS)
• Milner-Barry, Stuart 1
• Mimiambi (Herodas) 1, 2, 3, 4, 5
• Ministry of Economic Warfare (MEW) 1
• Mitchell, Joyce 1
• Moe, Helge (‘Mutt’) 1
• Montagu, Lieutenant-Commander Ewen 1
  • The Man Who Never Was 1
• Montgomery, Rev. William 1, 2, 3
• Moore, George Edward, Principia Ethica 1
• Moore, Miss 1
• Mountbatten of Burma, Louis, Lord 1
• Mussolini, Benito 1, 2, 3, 4
• ‘Mutt’ (Helge Moe) 1
• My Silent War (Philby) 1, 2