Many nights over the past eighteen months, stark footage of the Great Depression – shabby men in soup queues, emaciated families huddled in makeshift tents, destitute panhandlers – has flashed up on the TV news. Eighty years after the Wall Street Crash, as we seek to recover from the banking crisis of 2008, the pictures retain their ability to shock and frighten. Could it happen again? Is our generally comfortable existence really that vulnerable? The power of these images is instant: they are a shorthand for the fragility of the financial arrangements on which we depend.

The work of photographer Dorothea Lange played as significant a role as John Steinbeck’s The Grapes of Wrath in fixing in our collective memory the horror that – if we are honest – we fear may yet ambush us. And one picture resonates most: it shows an ‘Okie’,