Whoever gave this quote is a pro:
Asked to comment on the document, a senior British official, who spoke on condition of anonymity, said, “We do not discuss intelligence assessments.”
Reading these words, I can almost see the look of utter disappointment on the reporter’s face as he hears his informant tell him this after he agreed to keep the source anonymous. And then I see him thinking “Ah what the hell, I’ll use it” even though it adds nothing to the article.
Quotes don’t get much safer than that. Even if the source is revealed, who cares? On the reporter’s side, no one would ever know if this quote was fabricated. If you think about it, this is really a great quote for everyone involved, except for those reading it.