A bit off-topic, but this account about MI5 from a 2015 LRB article is great:

It was well known in the service that Roger Hollis’s secretary was also his mistress. When Hollis was director general, from 1956 to 1965, the first serial, or memo, seen by the night duty officer at MI5’s Curzon Street headquarters read: ‘Should the DG’s wife call, say one of the following …’ A range of possible answers was supplied, with a tick box next to each, such as: ‘The DG is in an extended meeting and will be home later.’