Lesson from History

The UK just released some formerly-secret papers regarding the activities of spies in the run up to the second World War.  I ran across the reference on the oxymoronically-named  History News Network.  They link to this story in the Financial Times:

Spy secrets failed to win Whitehall's trust
By Jimmy Burns
April 1 2005 03:00
[...]The use of spies was defended by Winston Churchill. But in remarks echoed six decades later in the controversy over the invasion of Iraq, Sir George Mounsey, secretary designate to the Ministry of Economic Warfare, challenged the value of the "sensational" information provided by agents.

"They have a secret mission and they must justify it," he said. "If nothing comes to hand for them to report, they must earn their pay for finding something." [...]

Of course, I can't claim to know the ins and outs of the spy business.  I wonder, though, if Sir George [no relation to the current White House occupant] was on to something.  Does the clandestine culture encourage -- or even permit -- people to come back and say, "I don't know, I couldn't find out."?