HSBC leaks Q&A: A global scandal or a storm in a Swiss tea-cup?

It has been described as the “biggest banking leak in history” – not least by the various European media outlets, including the BBC, that have been publishing some of the details this week. But where have the hundreds of thousands of files, which apparently detail industrial-scale tax evasion, come from? And what is the wider significance of the leak? Finally, where can we expect this scandal to go next?