Green’s Dictionary of Slang

Apollinaris mineral water, usu. as a mixer.

1878		Fun 26 Jan. n.p.: Sweet champagne and Apollinaris—Sham and Polly, as it is slangily called.
c.1895		E.W. Rogers [perf. Vesta Tilley] Scotch & Polly 🎵 Scotch and Polly, Scotch and Polly, jolly good stuff to drink / The Scotch got up in my head you know / The Polly got winking at me so.
1906		Harrington & Tate [perf. Vesta Tilley] There’s Only One London Town 🎵 Bring me that big Scotch-and-Polly! That's great.
1907		Otago Witness 15 May 73: We refreshed ourselves with a Scotch and Polly each.
1918		S. Rohmer Brood of the Witch-Queen [ebook] ‘A whisky and soda, or a burly British B. and S., even a sporty “Scotch and Polly”’.
1937		J. Betjeman in Night & Day 15 July 34/2: ‘Bet you that double Scotch and Polly, ole man’.