Curiously, the existence of this policy void, coupled with yet more scandal in his convoluted private life, does not seem to have done his reputation the slightest bit of harm. Despite strong Labour leads nationally and in London he won his re-election bid, somehow floating above the standard fray, categorised as a celebrity and amusing character who can reach parts of the electorate which conventional politicians struggle to get near. There are parallels with the SNP's Alex Salmond, another big figure whose public reputation is that of the jovial populist, when in reality, just like Boris, he is single-minded and driven to the point of monomania.

In Johnson's case, the books and highly entertaining columns ("like shaggy dog stories written by Cicero", in the opinion of another former colleague), appearances on Have I Got News For You, rugby tackling of opponents on the football field and assorted outrages have made him into the clown prince of the anti-politics movement.

Ask a Tory MP, peer or commentator with teenage children whom their offspring have been most impressed by hearing they have met and there is a fair chance that they will answer with one word: Boris.

For all the forced attempts at bonhomie, such fame does not endear him much to David Cameron or George Osborne. I was standing nearby when, shortly after Boris's triumph in the first mayoral election, the new mayor swept into the room. The Tory leader was elbowed aside by photographers keen to get a picture of the blonde bombshell. Cameron, who is good-natured but ultra-competitive, looked a little put out at being so obviously upstaged.

Cameron and Osborne seem fascinated by the Boris phenomenon, in the way that medical researchers are fascinated by the emergence of particularly virulent new strain of a disease which poses a serious threat to public health. Both make a not terribly convincing show of trying to appear relaxed about his rise, with the prime minister often wearing a forced smile whenever he and Boris are together on the campaign trail. The Conservative leadership wanted him to win re-election, of course, because defeat would have suggested that the Tory tide was going out. They also know that if he had lost Boris would have returned as rapidly as possible to the Conservative benches at Westminster and become a more immediate threat.