Green’s Dictionary of Slang

to inform (on), to betray.

1930		(con. 1910–20s) D. Mackenzie Hell’s Kitchen 168: Whether he was ‘lolly popped’ (peached upon) or whether he was ‘shopped’ ( given away by confederates) I am not sure.
1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 6: Lolly popped (or shopped): Give away.
1937		J. Curtis There Ain’t No Justice 126: ‘You might as well give us the tart’s monnicker.’ ‘All right,’ said Tommy. ‘Keep it under your hat [...]’ ‘All right. I won’t lollipop.’.
1960		J. Franklyn Dict. of Rhy. Sl.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
1989		J. Morton Lowspeak.