Green’s Dictionary of Slang

(UK prison) one who helps share or divide up a ration of tobacco; a prisoner may take on a regular ‘carvie’ for periods of his sentence; thus a trusted friend.

1950

P. Tempest Lag’s Lex. 32: carvie. One who ‘carves in’ – one who shares part of a packet of tobacco by subscribing to a common pool. [Ibid.] carving china. Partner in a purchase of tobacco. ‘So-and-so is all right; he’s been my carving china (or carvie) for a long time.’ This is a strong recommendation and signifies trustworthiness.