ABSTRACT
Prediction is both art and science. US Secretary of Defence Donald Rumsfeld famously observed that, 'there are know n knowns; there are things we know we know. We also know there are know n unknow ns; that is to say we know there are some things we do not know. But there are also unknow n unknow ns, the ones we don 't know we don 't know. And if one looks throughout the history of the UK and other free countries, it is the latter category that tend to be the difficult o n es.'1
