21.—(1) A head may refuse to grant a request under section 7 if access to the record concerned could, in the opinion of the head, reasonably be expected to—

(a) prejudice the effectiveness of tests, examinations, investigations, inquiries or audits F39[conducted by or on behalf of a public body] or the procedures or methods employed for the conduct thereof,

(b) have a significant, adverse effect on F39[the performance by a public body of any of its functions] relating to management (including industrial relations and management of its staff), or

(c) disclose positions taken, or to be taken, or plans, procedures, criteria or instructions used or followed, or to be used or followed, for the purpose of any negotiations carried on or being, or to be, carried on by or on behalf of the Government or a public body.

(2) Subsection (1) shall not apply in relation to a case in which in the opinion of the head concerned, the public interest would, on balance, be better served by granting than by refusing to grant the request under section 7 concerned.