When we published, in January, an early warning over the rapid growth and increasing complexity of Exchange-Traded Funds, we had little idea how widely-shared the concerns would become. Regulators have been making worried noises for months, and now even the popular media has caught on.

Today, it's the turn of BBC Radio 4, whose File on 4 programme will broadcast an edition tonight entitled 'Business as Usual', which criticises a return to complex and opaque products in the financial sector. One of its targets? Synthetic ETFs.