In the recent case (April 2009) of the Home Secretary (Secretary of State) v AHK, GA, AS, MH, FT and NT, this very subject matter was discussed; starting at Paragraph 12.
(1) A person may apply, without notice, for an order permitting him to withhold disclosure of a document on the ground that disclosure would damage the public interest.
(2) Unless the court orders otherwise, an order of the court under paragraph (1) –
(a) must not be served on any other person; and
(b) must not be open to inspection by any person.
(3) A person who wishes to claim that he has a right or a duty to withhold inspection of a document, or part of a document, must state in writing –
(a) that he has such a right or duty; and
(b) the grounds on which he claims that right or duty.
(4) The statement referred to in paragraph (3) must be made –
(a) in the list in which the document is disclosed; or
(b) if there is no list, to the person wishing to inspect the document.
(5) A party may apply to the court to decide whether a claim made under paragraph (3) should be upheld.
(6) For the purpose of deciding an application under paragraph (1) (application to withhold disclosure) or paragraph (3) (claim to withhold inspection) the court may –
(a) require the person seeking to withhold disclosure or inspection of a document to produce that document to the court; and
(b) invite any person, whether or not a party, to make representations.
(7) An application under paragraph (1) or paragraph (5) must be supported by evidence.
(8) This Part does not affect any rule of law which permits or requires a document to be withheld from disclosure or inspection on the ground that its disclosure or inspection would damage the public interest.