For urban migrants sending money home to their villages, and for people used to queuing at banks for hours to pay bills or school fees, the M-PESA money-transfer service, operated by Safaricom, Kenya’s largest mobile operator, is a godsend. No wonder it is used by 9.5m people, or 23% of the population, and transfers the equivalent of 11% of Kenya’s GDP each year; or that it has inspired more than 60 similar schemes across the world.