The same lessons are being learnt in a different context, that of financial services for the very poor. In the 1970s, pioneers in Latin America and Bangladesh – most famously Muhammad Yunus of Grameen Bank – demonstrated the importance of affordable credit for the poor, and discovered that poor borrowers could reliably repay loans. The early experiments grew into a worldwide microcredit movement.

But just as we were rudely reminded that there is more to our banking system than cheap mortgages, so microcredit experts have been realising that there is more to microfinance than loans for the poor: savings, insurance and payment systems matter too.

The trouble with living on two dollars a day is that you don't actually get two dollars a day. One day you might get five, then nothing for the next three days. Income is unpredictable. Outgoings, too, are irregular. Emergencies crop up. Under the circumstances, the most basic financial product, such as an easy-access savings account, would be invaluable.