Boris Johnson and David Cameron have created a Tory opportunity

Among many other things, the London Olympics were a brand launch – on a global scale – of Boris©. There were books, as there were before Barack Obama ran (the dividing line between a politician’s book tour and a campaign sweep is blurred to the point of non-existence). In March last year, there was a Michael Cockerell documentary in which Boris, for the first time, conceded that his ambitions did not end at City Hall: “Obviously, if the ball came loose from the back of a scrum – which it won’t – it would be a great, great thing to have a crack at.”

The present occupant of No 10 gave a great deal of thought to his response to all this. Most of the time, the relationship between the two Etonians has been one of friendly mutual teasing. As he ascended the stairs at Downing Street, Boris would enjoy pointing out how many former prime ministers were, like him, King’s Scholars – clever scholarship boys – rather than regular Oppidans like Dave. Since the arrival of Boris’s younger brother Jo as policy chief, the senior Cameroons have amused themselves by baiting the Mayor about the meteoric success of his sibling. “So which of you is it going to be?” they ask Boris. “You can’t both go for it, can you?”

Among all this public school badinage there lay a serious political trap, as Cameron grasped. “I am not going to be the person who didn’t want Boris back,” he told George Osborne. This was an astute judgment. For all the intermittent irritation that the Mayor has caused No 10 – some of it provoking furious private messages from Dave to Boris – there has never been any percentage in Cameron resisting his return to the Commons. Indeed, to seem anything other than wholly enthusiastic about that prospect would be a deadly sign of weakness. The PM understood that the only sustainable counter-strategy to the Boris fiesta was to join in the dancing and hug him close.

It is true that No 10 was not specifically expecting Wednesday’s announcement. Those around Cameron believed Boris still to be uncertain, nervous about breaking yet another promise. In 2012 he told the Evening Standard that, if re-elected as Mayor, he would focus on London’s problems to the exclusion of all else: “Keeping that promise cannot be combined with any other political capacity.”

Yet fidelity, it must be said, has never been prominent in Boris’s basket of political attractions – though he should not interpret the indulgence of public and party as a blank cheque for all time. Breaking a promise not to raise VAT, say, or (as Nick Clegg learnt the hard way over tuition fees) not to raise the cost to voters of a public service is very different to porkies about your political ambitions.

Does this mean Boris is certain to be Tory leader one day? By no means (as he would readily admit). He has no parliamentary base, although that could change in an instant if the polls showed that his leadership would improve his party’s fortunes. He is admirably candid and economically literate about the merits of immigration – far distant from the centre of gravity of Tory opinion on this pulsing issue. Don’t forget, too, that the Conservative Party has a perverse history of rejecting its front-runners, conference darlings and superstars. Ken Clarke, Michael Heseltine, Michael Portillo: all, for different reasons, were denied the chance to lead.

In the dark recesses of the Tory oligarchy, there is also a powerful “Stop Boris” urge that has many roots, ranging from unfiltered jealousy to a fear of ambition without purpose and a distaste for politics as showbusiness. When the day comes – if the day comes – it will be fought between the reservations and suspicions, let loose into the political bloodstream like a toxin, versus the juggernaut of Boris’s popularity.

The Conservative movement must now decide how it wishes to handle these new circumstances. Boris’s return need only be a problem if it is seen as a zero-sum game: if every time Boris does well, Cameron is perceived to have lost, and vice versa. The Tory party must learn to contain its impatience, too. It still resents Dave for the Coalition, for gay marriage, for the rise of Ukip. Boris has been a strong critic of the alliance with Clegg. But he was also an eloquent supporter of same-sex marriage and is, if anything, more liberal than Cameron on immigration (the prime issue driving Ukip’s success).

Boris’s announcement was, first and foremost, a release of human energy. It suggested that the Conservative Party is still fizzing with options and life, that it has strength and depth, and a gravitational pull to talent. The Mayor could yet make a difference to the general election if he complements Cameron, and is seen to do so.

Thus far, the Mayor and Prime Minister have behaved with shrewd restraint and handed their party a rare opportunity. What matters now is that their fellow Tories have the political maturity to grasp it.