charlie, adj. — Green’s Dictionary of Slang

charlie adj.

wary; frightened, cowardly; thus turn charlie, to become frightened [charlie n.¹ (1) or charley (howard) n.].

1958		F. Norman Bang To Rights 60: I was dead charlie and little fairies were having a right game in my guts.
1959		F. Norman Stand on Me 49: Now in those days I used to be a bit charlie of the law.
1969		(con. 1911) A. Baron King Dido 104: ‘Show you ’oo’s charlie.’ ‘All right. You ain’t charlie?’.

turn charlie (v.)

to act in a cowardly manner, esp. when one thus lets down one’s companions.

1951		Sunderland Dly Echo 2 Apr. 2/3: ‘Cor, it don’t ’arf beat me,’ muttered Cockney. ‘Enough ter mike me turn Charlie [...] Turn Charlie — git frightened, see?’.
1984		Partridge DSUE (8th edn) 199: [...] since ca. 1930.