asked the Secretary of State for Northern Ireland if he will list those topics on which it is not his practice to answer parliamentary Questions; and if he will list any changes in practice since 1972, indicating in each case the date on which the change was made and the relevant reference in the Official Report.

It is not possible to provide a definitive and exhaustive list of Questions which I might exceptionally decline to answer on grounds other than cost. Each Question will continue to be considered on its merits, but in some cases information is withheld for security reasons—see, for example, the reply given on 6th February to the hon. Member for Londonderry (Mr. Ross).—[Vol. 943, c. 447.]