Green’s Dictionary of Slang

over n.

[SE over, an extra, a remainder; note mid-19C banking jargon overs, odd money remaining after the daily accounts are made up, and which is divided among the clerks]

(UK Und.) in pl., proceeds of a theft that can, if not carefully disposed of, become vulnerable themselves to further theft, poss. by one of the gang.

[UK]D. Powis Signs of Crime 195: Overs Surplus of property or money after a theft that can itself be stolen by trusted persons.
[UK]J. Morton Lowspeak.