Tory front bencher Nick Hurd had, coincidentally I assume, asked a PQ to see when this procedure was last used. The answer is illuminating.
Mr. Hurd: To ask the Secretary of State for Communities and Local Government whether any written instructions have been provided to the Accounting Officer for his Department and its predecessors in accordance with paragraph 5.5 of the Ministerial Code since May 1997.
Barbara Follett: The accounting officer for the Department for Communities and Local Government has not obtained a ministerial direction since the Department was established in May 2006. I am not aware that any ministerial directions were issued to accounting officers of CLG's predecessor Departments in respect of the Department's current responsibilities since May 1997.
Hansard, 10 February 2010, col. 1028W
So, such correspondence is unprecedented. It's from the horse's mouth. Not that I am calling Barbara Follett a horse. Although she is rather good at troughing. Too the tune of £42,000.