I'm re-reading Patrick Hamilton's novel The Midnight Bell at the moment, set in a London pub of that name in the early 1930's.
Most of the action takes place in the saloon bar, overseen by the Governor and the Governor's wife and patrolled by the waiter Bob who gives his orders to Ella, a barmaid secretly in love with him. The public and private bars are described as "dreary, seatless, bareboarded structures wherein drunkenness was dispensed in coarser tumblers and at a cheaper rate to a mostly collarless and frankly downtrodden stratum of society". The public bar is also where mild would have been sold.
In the first chapter, the pub is about to re-open at five o'clock in the evening. As the regulars drift back in, they place their orders at the bar or with the waiter: half a Burton, a bottle of Bass - once staple drinks which it'd be hard to find in pubs now - a pint of bitter, and finally, "B an' B, please...He employed the popular abbreviation for Bitter and Burton mixed, and Ella gave it him, primly and deprecatingly, and took his money."
Richard Boston in his 1976 book Beer and Skittles lists some popular mixed drinks:
"Black and tan: stout and bitter
Mother-in-law: Old and bitter
Boilermaker: Brown and mild
M and B: Mild and bitter
Narfer narf: Half a pint of mild and half a pint of bitter
Lightplater: light and bitter
Granny: Old and mild
Blacksmith: barley wine and Guinness"
Black and tan made with a bottle of Bass and Guinness is apparently still quite popular in the United States.
In the Holt's house I drank in as a teenager, quite a few of the older drinkers would add a bottle of brown ale or Guinness to their draught beer. I never really saw the point as the cask bitter and mild were always well-kept (the practice of mixing bottled and draught beer probably has its roots in drinkers wanting to give some artificially carbonated life to poor quality cask beer) and the only time I drank anything else was the odd bottle of Guinness at the end of an evening.
I've got a few bottles of Schlenkerla Rauchmärzen and Lees Manchester Star Ale which are approaching their best before dates. I might try making a Franconian-Mancunian black and tan with a couple of them.