128 oz to US gallon. 4 quarts at 32 oz each, 2 pints per quart at 16 oz each, 8 oz to a cup and 2 cups to a pint.
Imperial gallon has two more pints, so an additional 32 oz, making an imperial gallon 160 oz.
When we were last in London we were looking at rent prices at Estate Agents and they seemed sort of inexpensive until we were told that the price was per week. Gak. I expect they'd have to call in the paramedics if they gave you guys the price of gas per gallon.