In an extraordinary year for British politics the gloriously unexpected triumph of Jeremy Corbyn in the Labour Party’s leadership election in September 2015 probably ranks just behind ‘Brexit’ on the political Richter scale. To recall, Corbyn is known for his far-left political sympathies, his total indifference to fashion, and his propensity to rebel against his own party while Blair was in power – over 400 times, according to my former colleague Phil Cowley. He was only nominated for the leadership by elements of his own party to give some breadth and interest to a leadership election that would otherwise have featured three identikit figures from the centre and right of the party. His chances of winning the leadership were initially placed at 1000 to one, odds which, at the time, did not seem particularly generous.

In a turn of events that made Leicester City’s triumph in the English Premier League seem predictable, Corbyn trounced the opposition in a landslide victory that has variously alienated his own parliamentary party, energised anti-austerity activists, and allowed the Conservative Party to ride out its own post-Brexit ructions untroubled by effective opposition in Parliament. How did this happen?