I'm referring to the document Accountable Government, Chairman. It's issued by the Privy Council Office under the authority of the Prime Minister. Questions about interpretation and application are usually answered by the Privy Council Office. In the case of ministers, though, the Prime Minister is ultimately responsible for ensuring that a minister has or has not complied with it. In the case of members of the political staff, it would be each individual minister who is responsible for ensuring that his or her employees comply with it, or for dealing with any cases of non-compliance.
On April 13th, 2010. See this statement in context.