Green’s Dictionary of Slang

ha’penny n.

[usu. middle-class euph.]

the female genital area.

[UK]Partridge DSUE (8th edn) 529: [...] C.20.

In phrases

keep your hand on your ha’penny (till the right man turns up)

advice to young women to retain their virginity until the advent of ‘Mr Right’.

‘Novareinna’ Penumbra 🌐 You disgusting trollop! [...] You’ll not make a laughingstock out of me because you didn’t have enough sense to keep your hand on your ha’penny!