What is the connection between American firm Covington & Burling and the British secret service? A reputation for undue secrecy, paranoia and for playing their cards close to their chest in the face of expert foreign competition? Partners who fantasise about being James Bond?

Alas no. Covingtons’ plush Mayfair offices, where the firm was until last week bunkered down, used to be an MI5 office. A spokesperson for the firm said the building’s features included plenty of soundproofing and a windowless basement that looked “a lot like an interrogation room”. (The Diary shudders over the possible fate of any junior assistants who failed to meet Covingtons’ billing targets.)