Traditionally and stereotypically, British culture and particularly upper class British culture is supposed to particularly value fair play. Torture would presumably violate this valuer.
"Blimp" is a nickname often used (particularly in the period of say 1850-1950) for a British officer, particularly a Colonel (the standard phrase was "Colonel Blimp"). It suggested an officer from an upper class background, who was pompous and ineffectual. Thus the sentence suggests that the soldier favors obtaining information by torturing prisoners, while the officer objects to this, and says also that the officer's view is outdated, and by implication, that the soldier's view is better or at least more modern.