(1) Subject to the provisions of this section, a head shall refuse to grant a request under section 7 if -
(a) the record concerned contains information given to a public body in confidence and on the understanding that it would be treated by it as confidential (including such information as aforesaid that a person was required by law, or could have been required by the body pursuant to law, to give to the body) and, in the opinion of the head, its disclosure would be likely to prejudice the giving to the body of further similar information from the same person or other persons and it is of importance to the body that such further similar information as aforesaid should continue to be given to the body, or
(b) disclosure of the information concerned would constitute a breach of a duty of confidence provided for by a provision of an agreement or enactment (other than a provision specified in column (3) of the Third Schedule of an enactment specified in that Schedule) or otherwise b