Green’s Dictionary of Slang

1. (UK prison) drawing attention to oneself so as to allow a confederate to break prison rules unnoticed.

1933		C.E. Leach On Top of the Und. in DSUE (1964).
1954		J. Phelan Tramp at Anchor 39: I began to learn the twiddle, the dairy, the cop and pass.

2. exposure, publicity.

2000

W. Birch No Sleep Till Canvey Island 249: Ian was an editor’s dream come true, so he was bound to get the dairy.