The Sketch: Boris mixes a new sense of purpose with his old charm

You wait years for a prime ministerial Tory, and then two come along at once. Both unlikely in their separate ways, one rather more unlikely than the other. Neither professional politicians; both representing "change". One in Parliament and the other in City Hall. Any closer and the order of precedence gets confused. Remember, they are Etonians, and their amiability amateur spirit and old-fashioned good manners are all mounted on the same hyper-alloy combat chassis.

Boris was in front of the Culture Select Committee yesterday. Last year, he was a humorous celebrity; this year he fired, by sheer force of personality, the most powerful policeman in Britain. He is also in charge of a £9bn budget to host the world's largest sporting event. It's an extraordinary transformation. He has lost just enough of his manner to allow the matter to come through. And you can see as you watch his small, clever eyes how many opportunities for humour he passes over in every beat of the conversation.

Humour, as a by-product of the business in hand, is a great charm. The committee was determined not to be charmed. The MPs reckoned the Mayor was Toad, and they a collective Badger. They liked to use expressions such as "The National Lottery Distribution Fund" in order to convey a sense of seriousness.

Boris doesn't convey a sense of seriousness but he does a sense of purpose well, while using light-hearted expressions like "pari passu". Asked if there were tensions between himself and Lord Coe, he said: "It's a feast of reason." And, never before seen in this part of the world – he entertained a new idea, put to him by the Labour MP Alan Keen. He suggested shafting the Olympic Committee and presenting a sort of low-cost games that the Third World could subsequently host. You could see him being tempted. And in public. A great democratic virtue.

It's surprising who turns out to have the goods. Cameron, Johnson, Miliband all might have seemed much of a muchness in their backroom days. But the first two turn out to be leaders; the third – no one knows. The levity is gone but not to make way for gravity. No, he's giving us instead a sort of thin-lipped, fast-talking, finger-jabbing, staring intensity. I don't want to sound hard to please, and admit it's a great improvement, but it's still not quite right.

simoncarr@sketch.sc

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