Cameron said today he had passed on to European partners information gleaned from intelligence in cooperation with US and other allies that had helped avert terror plots.
He said anger at revelations US spies listened in to calls on German Chancellor Angela Merkel's mobile did not mean governments should legislate to rein in "properly funded intelligence services".
Cameron endorsed an EU summit statement backing French and German moves to negotiate a new understanding on the rules of the spy game with Washington by the end of the year.
The publication of the Snowden files "is frankly signalling to people who mean to do us harm how to evade and avoid" detection, he said, citing a massacre in a Kenyan mall in which at least 67 people died.
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"It is going to make our world more dangerous," Cameron said.
To avoid tilting the balance in the fight against terrorism, Cameron maintained that this "means not having some lah-de-dah, airy-fairy law" drawn up at European Union level in Brussels to constrain spy operations with global importance.
"I've lost count of the plots I've seen, information I've seen," Cameron said of intelligence reports landing daily in his lap.
"And I've shared that information with other European countries," he underlined, pointing out that the Snowden leaks are making it "a lot more difficult to keep our people safe".
Cameron said he was "very struck how colleagues don't want a breach in this relationship," calling the plans put forward by Merkel and French President Francois Hollande "good and sensible".
He refused to comment when asked if he was satisfied his own mobile had not been tapped or if he could give Merkel assurances that he had not seen reports from US partners detailing private telephone calls on her mobile.
Cameron insisted that the intelligence services in Britain are subject to the fullest possible democratic scrutiny.