I've seen in the Acton Museum Depot a Tube ticket machine that dispensed tickets for various destinations (I'd say at least as far as current zone 3) for 40p. The guide couldn't tell the exact period, albeit he said he wasn't very old. I'd say late '70s, what do you think?Update:I've got a picture of the machine, and after examining it I've to say that all the destination were actually in zone 1. Used Google Books and found out that 40p was the price of the cheapest single ticket in 1982. Mystery solved!. Created by Barbara J. cars-transportation-en - rail-en

I would agree sometime during the 1970s. Tube fares were once much cheaper - when I started work in 1960 a weekly season ticket between Edgware and Tottenham Court Road on the Northern Line cost me 19shillings and 11 (old) pence (that's actually half way between 99p and £1). Wouldn't get you very far today, I'm afraid!