For someone who's seemingly valued caution and control above all other political virtues, Theresa May's decision to call an early election on June 8 came as something of a surprise.

Not only has May broken what John Howard might once have described as a "non-core promise" (she had repeatedly pledged to see out a parliamentary term scheduled to end in 2020) but she is relying on the bullish forecasts of opinion pollsters (whose failure to predict the outcome of recent votes is matched only by the inability of economists to forecast the financial consequences of Brexit).