Think of the two elections that have bookended this momentous political decade and the images they conjure — potent symbols of how politics has changed. The first is of a sun-dappled day in the Downing Street garden in 2010, when David Cameron and Nick Clegg stood shoulder to shoulder at the consummation of their coalition, laughing and joking with the easy charm of public schoolboys born to rule, which, of course, they were. After the near permanent psychodrama that characterised Gordon Brown’s battles with Tony Blair and then with himself, it felt like a breath of fresh air, proof that people of different political stripes can work together.

Think now of this month. Of Nicola Sturgeon pumping her fists with glee as Jo Swinson —