Green’s Dictionary of Slang

1. (Aus.) a number.

1992		R. Puxley Cockney Rabbit.
2002		Pete’s Aussie Sl. Home Page 🌐 cucumber: a number.

2. (UK prison) voluntary segregation under Rule 43 for the protection of vulnerable prisoners, usu. sex offenders.

2014

Eve. Standard (London) 8 July 14/2: ‘Take the cucumbers, Jonno! It’s your only of surviving in this nick. Take the bloody numbers!’ [...] In prison lingo cocumbers = numbers; numbers = Rule 43; Rule 43 sdays that any new arrival is entitled to bes egregated for his own protection on a vulnerable prisoners (VP) wing. VPs are mainly sex offenders or ‘nonces’.