The Prime grin-ister does his Boris face

Smile, though your heart is breaking: Boris Johnson and an upstaged David Cameron (Getty Images)

Cameron-watchers have become used, in recent months, to seeing That Smile on the Prime Minister's face. It means Boris Johnson is nearby and has upstaged him once again. Their fractious relationship dates back to Eton and Oxford, but has become more urgent of late, as Cameron feels the chill hand of peer disapproval around his heart and worries about his old friend's ambitions.

When they appear side by side these days, they're like a posh-Tory Laurel and Hardy – the thin one worrying that he's become straight man to the fat guy. Or like two teenage BFFs, one of whom suddenly wonders if she's been the other's Plain Friend all the time.

The speeches at the parade said it all. Cameron went for earnestness, invoking England's past and future and praising the Paralympians as role models. Boris went for sex jokes: the Games had come to "a tear-stained and juddering climax" after weeks in which the nation rapturously shagged on the sofa. The audience roared. Cameron, the insipid warm-up man, smiled frozenly.

How galling it must be to reflect that, however important the bridegroom is on the day, however fervently he thanks everyone for the presents and flowers, he'll always be upstaged by the Best Man.