Green’s Dictionary of Slang

(UK milit.) selling or buying liquor illegally, thus bagdadder.

1877		H. Hartigan Stray Leaves (1st ser.) 94: ‘[D]on’t you be goin’ to the canteen, or Bagdaddin (all old soldiers know what that means—getting grog on the sly.
1879		H. Hartigan Stray Leaves (2nd ser.) 8: They often did carry their ration of liquor away [i.e. from the canteen]; and in consequence there was any amount of ‘bagdaddin’’ (selling liquor under the rose) .
1879		H. Hartigan Stray Leaves (2nd ser.) 27: This [...] brought him more custom than all the ‘bagdadders’ in the station.
1879		H. Hartigan Stray Leaves (2nd ser.) 312: [He went] to a ‘bagdaddin’ establishment for the purpose of procuring the liquor.