You will note the jump in prices between the early seventies and the late seventies.
That is because it spans the 1973 Arab-Israeli conflict, the formation of OPEC, and the resulting surge in fuel costs. I worked in a petrol garage in 1972 and 4 star was 33 pence per gallon and had changed little in the previous decade. Eighteen months later it had tripled in price and it has been climbing ever since.