With a world economy burdened by debt and many countries beset by one banking scandal after another, the appeal of debt-free and supposedly ethically spotless Islamic finance seems to be growing. Estimates by the Asian Development Bank and Islamic Financial Services Board (IFSB) put its size at $1.9 trillion in 2014 – still small by conventional standards (and with around a third of that money in Saudi Arabia assets) – but global consulting firm EY reckons it grew at an average of 17.5% a year