Ball in his court: Johnson squares up to his old rival David Cameron in Trafalgar Square for International Paralympic Day, 8th September

“This job is the most engrossing I’ve had,” Boris Johnson told me in early September. London’s mayor acknowledged that it took “a year or so” for him to appreciate the role, after beating Ken Livingstone in 2008. As mayor of the capital, directly elected (unlike the prime minister or cabinet members) by nearly 1.2m people, Johnson has the biggest mandate of any politician in the country. Recent polls show he is set to be re-elected with a comfortable majority next May, even according to Labour’s own private figures.

These ratings put force behind the question that has hummed around Westminster for three years, spurred by Johnson’s repeated clashes with David Cameron. Will Johnson try to succeed his old rival and fellow Conservative as prime minister?

“Look, what I have said is that I won’t go on [as mayor] after eight years,” Johnson said when pressed. “I think you can go on too long.” What about cutting short the eight years? “No.” So he will serve a full second term? “You betcha!” Suddenly, he sounds more like the Wodehousian figure many adore. Asked whether he could serve as both an MP and mayor, he declined to comment but gave a low laugh.

Many political insiders believe he has a game plan: to stand as an MP, either at the 2015 election or in a by-election after his second mayoral term ends in 2016, and succeed Cameron as Tory leader. That would make him an eventual threat to George Osborne, Cameron’s heir apparent, as well as a continual source of trouble for the prime minister. Prospect has learned that Johnson opposes Cameron’s policy of evicting council estate tenants guilty of participating in August’s riots, questioning how displacing the poor onto the streets fits into a drive to fix “broken Britain.” This is merely the latest in a long list of public and private disagreements with the prime minister.

The Boris dilemma is not just about whether Johnson has reached the limits of his ambition: whether the powers of mayor seem to him like adequate return for such an extravagant endowment of charisma. It is also about whether such a rebellious personality, suited to the big-character canvas of a capital city, disqualifies him from the calculation and compromise of national politics—and…

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