How to answer by not answering

Masterful. Simply masterful. Worthy of Sir Humphrey.

"Mr. Howard: To ask the Prime Minister pursuant to his statement on Europe, of 20 April 2004, Official Report, columns 155–57, what factors he took into account in reaching his decision on whether to hold a referendum.

"The Prime Minister: The factors leading to the Government's decision to hold a referendum were set out in my statement of 20 April 2004, Official Report, columns 155–57."
(Hansard, 4 May)