Green’s Dictionary of Slang

iron tank n.

a bank.

1960		J. Franklyn Dict. of Rhy. Sl.
1968		J. Alard He who Shoots Last 216: You ain’t stuck up no iron tanks before.
1971		J. Jones Rhy. Cockney Sl.
1984		Partridge DSUE (8th edn) 397: since ca. 1918.
1992		R. Puxley Cockney Rabbit.
2002		B. Kirkpatrick Wicked Cockney Rhy. Sl.