Apparently gin and mild is an old man's drink - but I need to get it for a relatives birthday, anyone know a nick name for this drink ?
There is a drink called the Hangman's Blood that uses either porter or stout, which aren't too far off of a mild (well, the porter at least). It also contains other things like rum and brandy so it might not be what you're thinking of, but it does have a history that goes back to around 1930 or so.
The name for a mixture of dark beer and gin (plus brown sugar) is a Dog's Nose. It was usually not mild but porter in the 19th century. It was heated with a little nutmeg on top. Dickens refers to it in Pickwick's Papers. By the 20th century it was still drunk in the East End but with Mild instead of porter and no sugar, nutmeg or warming.