If you've read Charles Dickens' David Copperfield, you'll be familiar with the outlook for the impecunious Mr Micawber, namely: "Annual income twenty pounds, annual expenditure nineteen six, result: happiness. Annual income twenty pounds, annual expenditure twenty pound ought and six, result: misery."

In some African countries milk is packaged in bags. The bags go into a jug and into the fridge. Cut off the corner of the bag and the milk can be poured via the jug. "It's their equivalent of the milk bottle, if you like," says Chris Bolton, sales and operations director at PFM Packaging Machinery.