Nick Robinson: I underestimated Boris

Boris Johnson personally raised the prospect of taking legal action against the Government with David Cameron to speed up a review of London airport expansion. (Getty Images)

"I knew Boris at Oxford", writes Nick Robinson for the BBC, "I never thought for a minute that he'd be a politician". Many years later the Beeb's political editor also pooh-poohed the idea of Boris running for mayor.

Now Robinson is changing his tune. Boris is a threat to Cameron. His decision to criticise the reshuffle confirmed the mayor's position as distinctly and dangerously off-message.

Now "everything he says and does...will be seen through the prism of his scarcely-concealed political ambition." And the next few years of Tory politics will be defined by how Boris and Cameron learn to live together.