Green’s Dictionary of Slang

sixpenny n.

a pint of beer costing sixpence.

1822		Public Ledger 4 Nov. 3/4: On 28th of May last he was employed by Barnett [...] to go to the defendant’s house to purchase a pint of sixpenny.
1859		G.A. Sala Twice Round the Clock 291: Comes here every morning regular. Pint of mild sixpenny; bird’s-eye; gives the waiter twopence, and goes away.
1868		Bristol Dly Post 15 Sept. 3/3: They drink their own jiolly good healths in half a pint of sixpenny!
1874		J. Greenwood Wilds of London (1881) 141: Stimulated by a pint or so of that excellent tradesman’s potent ‘sixpenny’.
1880		Buckingham Advertiser 30 Oct. 4/6: ‘Which would you rather have, a pint of sixpenny or a pint of water?’ (Laughter).
1904		Manchester Courier 29 Nov. 7/3: One member suggested that a pint of fourpenny would not do any of the inmates harm, and a pint of sixpenny would do many of them good.
1919		Tamworth Herald 29 Mar. 4/2: [He] said in cross examination that he asked for a pint of ‘sixpenny’.
1927		Western Dly Press 19 Sept. 4/4: Monday it would be ‘sixpenny,’ perhaps six or seven pints [...] Tuesday would begin with ‘sixpenny,’ and change to ‘fivepenny’ after nine o’clock.

In compounds

sixpenny dark (n.)

a glass of port.

1963

R. McGregor-Hastie Compleat Migrant 18: Sly grog [...] is popularly supposed to be drunk by dings and dagoes, when they are not knocking back the ‘sixpenny dark’ (cheap heavy port) sold in pubs.