To say that this is standard behaviour for a politician is to fall into a lazy cynicism. As Johnson's old opponent Neil Sherlock said, most people are in politics for a reason. They want to fight the European Union, balance the budget, defend the National Health Service or redistribute wealth. The irony of Johnson's career, which the uncomprehending media have missed despite all the coverage they have given him, is that he is far more of a calculating careerist than the tired politicians from the analogue age he and his kind are meant to have supplanted. And the old politicians know it. Alone among the power elites of Britain, they could see him for what he was.

While Johnson charmed and conquered Eton, Oxford, the press and the BBC, the one institution his brand of celebrity Conservatism failed to impress was Parliament. "The Commons sees through you in a way that other institutions don't," said Quentin Letts of the Daily Mail. "It could see through the accent, and the fact that he was trying to ventilate false anxieties about matters in which he wasn't really very interested. The reaction was quite often silence. You see, Boris isn't angry. You've got to be angry: you've got to feel things as an MP, but there is no soul, no church in him. No belief. Most people don't just go into politics out of vanity, but maybe he has."

Johnson has recently tacked again and is posing as a right-winger, as he manoeuvres to become the next leader of the Conservative Party. If I were a Tory, I would believe in Father Christmas before I believed in him.

On the rare occasions when journalists challenge Johnson about his flexible behaviour, he cites as his role models Disraeli and Churchill, who notoriously changed their minds and, in Churchill's case, changed his party. Both were indeed great politicians. But the flexible politician may be a man who recognises changing circumstances and resolves to change with them, or the man who will do anything to maintain his position. As I finished Purnell's exhaustive biography, I wondered why the British think him worth the attention and why Time magazine described him as one of the 100 most influential people on the planet. What has he achieved? What great or even good book has he written? What principle has he promoted beyond his own self-advancement? Far from following Disraeli or Churchill, Johnson takes his lead from an altogether less inspiring predecessor. As he shifts and plots to remain the centre of attention, I can hear him singing to himself:

And this is law, I will maintain
Unto my Dying Day, Sir.
That whatsoever King may reign,
I will be the Vicar of Bray, Sir!