The role of a Chief of Staff

In the fictional US TV series 'The West Wing', the President's chief of staff Leo McGarry once said:
"I take a bullet for the President. He doesn't take one for me."

Having seen David Cameron reveal how his chief of staff, Ed Llewellyn, had received information on alleged phone hacking from The Guardian, but 'failed to pass it on' to the then leader of the opposition, it appears Cameron agrees with this sentiment.