Ministers are responsible to Parliament, Chair, for ultimately all matters within their jurisdiction, including the policies of the government and the appropriate conduct of officials in their departments. By convention and in many cases by formal instrument of delegation, those authorities are delegated to departmental officials. That is often spelled out in the regulations to statutes and sometimes in the statutes themselves.
By convention, ministers are responsible for policy and officials advise ministers on policy. Officials are responsible for the administration of their departments.