"I never instructed a briefing against the Chancellor."
But what if one of his attack dogs asked if he could give the Chancellor a kicking and the Prime Minister did not demur. Is that "instructing a briefing"? Probably not.
Or suppose the Prime Minister said in the presence of his afore-mentioned attack dogs that someone should take the Chancellor down a peg or two. Is that "instructing a briefing"? Probably not.
Cameron was obviously conscious of these distinctions, asking at one point:
Will the Prime Minister get to his feet and tell us that he knew absolutely nothing about the briefing against his Chancellor?but, typically, he failed to press his attack home.