Travelcards were only introduced in the early 1980s - I can remember buying my first one at Borough, a colourful pre-printed card numbered something like 0000019 (I think I still have it somewhere*). The excitement of being able to travel around all day on tubes and buses without having to pay again!
Prior to their introduction, almost all tube and bus travel was single tickets, one per journey. Tube stations had ranks of ticket machines, each issuing a single value, with a list of the stations each was valid to on the sloping top of the machine.
In the late 1950s or early 60s, my family were staying with my grandparents, long term Londoners, and we went from Finsbury Park to Kew Gardens for the day. Coming home, for some reason we caught a North London line train instead of the tube, and were given a dressing-down by a ticket inspector for using LT tickets on a BR service. My grandmother gave as good as she got, and as far as I recall, we didn't pay extra, or have to get off the train.
In the late 1980s, I lived in Camden Town, and usage of the North London line was very low - dusty 2-car units (EPBs? HAPs?) with hardly a soul on them in the daytime.
(*edit - I knew I'd still have it)
View attachment 130469