Boris Johnson may be an uproarious byword for political priapism so far as the rest of the country is concerned but London is a more serious matter. The role of the mayor in a world-class city is different from that of a national politician. As Rahm Emanuel, mayor of Chicago, said in an interview last week: “I worked for two great Presidents. They talk about things they want to do — I’m doing it.” You can truly leave your mark on a city. Johnson’s powers are more limited than, say, the mayor of New York, but his championing of the capital is crucial. His power lies in the force of his personality.

In his new book The Wit and Wisdom of Boris Johnson, the author Harry Mount quotes MP Matthew Parris: “There is something about London — indefinable but you can feel, almost touch it — that makes an eccentric individualist with a touch of roguishness, a touch of the joker and a touch of genius, the best and perhaps only type of candidate that feels right.”

The trouble with mavericks who pitch themselves outside the political system is they can irritate those on the inside. David Cameron has always maintained that he is Ibiza-scale chillaxed about Johnson wanting his job but that doesn’t mean he will strew his path with palm leaves. Rather, it looks as if the Prime Minister is about to kneecap him in the Spending Review.

From what I hear, the budget cut for London transport is around 50 per cent, excluding capital projects such as Crossrail. Well, something has to pay for the High Speed Rail project, which will cost about £20 billion. A cut as gigantic as this means that Tube fares will have to rise, or the young and the old will lose their concessions, or night buses for London’s low-paid workers will be disbanded or the Mayor’s cycling vision has to be dumped. Which is it going to be?

This is the moment of reckoning: Johnson has to play hardball with the Government. If Cameron and Osborne have decided they no longer need to support him because he is not seeking re-election, then he does not have to return any favours. Why should he become chairman and cheerleader for the Conservatives at the next election?

The great election link between the Prime Minister and Mayor of London is Lynton Crosby, who ran Johnson’s campaign and is now running Cameron’s. I hope Johnson is running rings around him. There is too much attention paid to Johnson’s progeny and not enough to his legacy. A man of his gifts, ambition and vanity will not wish to be remembered as the mayor who failed London. By 2018 the capital will have a population of nine million. Anyone of working age knows their best bet is to head for London. If the transport is second rate or unaffordable it will cripple the city and the country’s GDP. Boris’s last mayoral battle must be to save London.

Bye-bye USA — hello China

An unforeseen consequence of America’s Space Race with the Soviet Union was that American women became better educated. The competition raised the stakes, right across populations. I hope there will be a similar China effect, and that competition will improve conditions for us all.

I have been reading Liam Byrne’s book Turning to Face the East, which begs the UK to shape up for the arrival of the Asian century. America may still look like the geopolitical leader but this disguises the economic ascendancy of China. It feel unnatural unhooking ourselves from the United States but perhaps now our foreign policies are diverging the cultural and economic ties will loosen too. Of course, we can learn a work ethic from China but friendship is harder. We understand America. How long will it take to say that about China? The first step is to make visas simpler. We cannot know the Chinese until we meet more of them.

All head and no heart — that’s Google

I am torn on the rights and wrongs of Google. I do not believe it is a monstrous organisation. It is delightfully innovative and has helped revitalise the East End. Its absolute belief in freedom is exhilarating. It is also wrong. Google has made the primary error of ignoring the heart in its obsession with the head. It has all the cool technology and lacks emotional intelligence. So it replies logically to the tax question that it does not make laws and is puzzled that the public do not accept this. Similarly on violence and pornography, it shrugs that it would be anti-freedom and futile to block sites. The trouble with Google is that it talks like a computer when it sometimes needs to respond as flesh and blood.

Better to keep shtum, old boy

I have not quite yet absorbed the implications of Michael Douglas’s Orpheus in the Underworld account of his sex life, which he described in order to explain his throat cancer. It is not clear to me whether it was intended as self-reproach or a righteous expression of selflessness? There is a suggestion of excess which somehow sounds ungallant towards his wife Catherine

Zeta-Jones. Also blending the cancer and the cure is confusing. I am all for medical transparency but the hurly-burly of the chaise longue should remain a private matter.