Green’s Dictionary of Slang

1. (UK prison) any form of contraband, letters, parcels etc, smuggled into a prison.

1958		F. Norman Bang To Rights 79: The screw gets the joie [sic] and sticks it in your peter.
1989		J. Morton Lowspeak.
1998		J. Hoskison Inside 26: A ‘joey’ is a parcel of drugs smuggled in on a visit.
2004		(con. 1988) N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 322: ‘Bottling’ is the universal way that prisoners hide items from searching by the screws. It involves inserting the parcel or ‘joey’ into the anus.

2. (drugs) a drug addict who works as a drug mule.

2002

Observer 17 Feb. 12: Not a user himself, he tried to avoid carrying drugs on his person, leaving his ‘joeys’ – addicted minions paid in fixes – to run the risks.

3. (UK drugs/prison) a bag of heroin, weighing either one gram or half a gram.

1999		J. Cameron Brown Bread in Wengen [ebook] Yes please one little ten-pound joey sir! And all they brothers get hooked.
2004		J. Archer Prison Diary 49: Heroin [in] a joey or a bag, which is about half a gram, can cost as much as £20. [Ibid.] 179: A gram of heroin [a joey] may be worth forty pounds on the street.