Green’s Dictionary of Slang

all right; usu. as phr. all harbour.

1897		Marshall Poems 46: Note. Learned Judges, worthy Magistrates and other Innocents, are informed that ‘all harbour light’ is cabby’s favourite rhyming slang for ‘all right.’ [F&H].
1938		(con. 1900s) in J.B. Booth Sporting Times 88: She said to herself [...] ‘It’s all harbour, I think they’ll do.’.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
2002		B. Kirkpatrick Wicked Cockney Rhy. Sl.