Green’s Dictionary of Slang

twopenny n.1

[rhy. sl.; twopenny loaf = loaf of bread; note the later loaf (of bread) n.]

the head, esp. in phr. tuck in your tuppenny.

[UK]G. Kent Modern Flash Dict. 19: Jemmy – twopenny, head.
[UK]Era (London) 2 Sept. 5/2: He tucked in his twopenny, squared his toes and elbows.
[UK]Hotten Dict. of Modern Sl. etc.
[Aus]Bell’s Life in Sydney 4 May 3/4: The undermentioned young gentlemen [...] ‘ducked their twopennies’ to the Water Police magistrate on Tuesday.
[UK]Hotten Sl. Dict.
[US]Letters by an Odd Boy 27: Tuck in your twopenny, and let me have an over before I begin!
[UK]Ally Sloper’s Half Holiday 14 June 53: [caption] Tuck in yer Tuppeny [sic].
[UK]A. Binstead Gal’s Gossip 104: After I had ducked my tuppenny to allow him to slip the neckband under my rear stud.
[UK]‘George Orwell’ Down and Out in Complete Works (1986) I 178: [note] ‘Twopenny’ is arrived at like this: loaf of bread – twopenny loaf – twopenny.