Can one imagine two more zoomorphic politicians? Ken Livingstone and Boris Johnson are both, for me, recent escapees from David Attenborough programmes. Ken slides out of Life in Cold Blood, like some Lambeth axolotl, emerged from underneath the stone to sit in triumph on top of it. Everyone who has attempted to kill off his career has been left only with a handful of tail and a vague feeling of having been made to look silly. Boris's series, David Attenborough's Life on a Warm Sofa: The World of Pets is as yet unmade, but would feature a smiling, boisterous Johnson destroying a house by knocking everything over, eating all the food and pooing in the beds.

Clearly, at the empathic level, one prefers the Tiggerish mammal. What is not to like about Boris? Whereas there is horrid Ken down the years: Ken and his “I was ahead of the game in talking to the IRA” self-whitewash; Ken and his fondness for Castro and Chávez; Ken and his denial over the downsides of certain visiting Muslim clerics; Ken and his description of any criticism of him or his staff as being a “smear”; Ken and his silly, petulant battles against Gordon Brown and Trevor Phillips; Ken and his absurd hangers-on, like the ridiculous Lee Jasper, soi-disant (and soixante-huitard) spokesperson for London's unconsulted “black community”.

This past few weeks we've also seen Ken and his champions. I think I know the Left and its strengths and foibles pretty well, but it was beyond foible for a signocracy of left-wing luminaries to create and lend their names to an “open letter” attempting to awake the British people to the almost fascist quality of the Johnsonian threat. “A battle,” they claimed, “is being waged in the country and it is time to stand and fight to ensure that Livingstone wins so that the ideals of democracy, equality and sustainability endure and are given new hope...” And so on.

It was one of those absurd internal bulletins that the Left sometimes sends itself in default of talking to the public. What person, after all, considering voting for Boris, will be swung back to Ken because the far-left Labour MP Diane Abbott recommends it? And anyone who thinks that the journalist Andrew Gilligan, now working for the Ken-loathing London Evening Standard, is “a battering ram... against the ideals of a more democratic, egalitarian and sustainable politics” does not understand Gilligan's complete lack of higher belief.

Like Ken, Boris has also offended, although he may not have meant to. The crass columnar references to “piccaninnies” and “watermelon smiles” were probably part of his only partly constructed self-deprecatory “oh crikey” act. He has, like Ken, fulfilled his daft quotient, joining the Plaid Cymru-inspired attempt to impeach Tony Blair and indulging in fairly standard contrarian diatribes against targets such as the city of Liverpool. Some of this barminess still leaches out into his mayoral website where - in a reverse Salmond - he lambasts “a Scottish Chancellor and a Scottish Prime Minister” for being somehow anti-London.

Many readers, having got this far, may well say one or both of two things: don't bother voting then, and who cares, anyway? Is this not all a metropolitan obsession, in which the media resident in a pampered capital try to get the 53 million of us who don't live in London, to care about the seven million who do? Well, I understand the sentiment - but, in Puritan spirit, I must recall you to yourselves, because the plain fact is that London does matter, and what happens there will affect most British people in some way or another.

Now, I originally thought Ken would be a lousy mayor, always show-boating, always blaming others if things went wrong, always setting up Utopian and expensive schemes that would then collapse. But it didn't happen. Instead we got the congestion charge, the most successful and courageous attempt to turn back the inevitable gridlock to which the city was condemned. London managed what Edinburgh and everywhere else flunked, and it was Ken who made it happen. The mayor got Londoners back on buses, Tube and bicycles at the expense of the cars that were killing the capital. Ken also helped to win London the Olympics, one of the most important and sought-after honours that any city can attain. Far from alienating the bankers and industrialists, Ken wooed them when necessary. Ken, wrong on all the things that don't matter in a London mayor, has been right on almost all the things that do.

Boris? Visit the website. In general Boris will do everything that anybody wants, and all for less money. There isn't much that is specific, but such stuff as manages to declare itself includes bringing back the old, dangerous Routemaster bus - the steam train of the bus-nostalgia world - and a commitment to “rephase traffic lights”, which is code for giving pedestrians even less time to cross the road, and motorists even more. This is almost the exact opposite of what we need to do, and might best be described as a uniquely anti-green and anti-child measure.

But there is another truth about Boris, one which I am reluctant to state, because it is both ad hominem and self-incriminatory. I recognise in myself someone who shouldn't really be allowed to run anything other than himself. I did once have delusions that I could be an executive, but the commitment to doing boring things, at high levels of detail, eventually defeated me. Even now my expenses go unclaimed, my occasional forays into other media remain uninvoiced, some solicitors of my services go long unanswered. And Boris makes me look like Mr Efficiency. There is hardly a senior soul in this business who hasn't turned up to an evening with Boris, to discover that it is an evening with anyone but. “I'm sorry,” says the chair, anticipating the boos of disappointment, “but Boris Johnson is unable to be with us,” followed by some lie.

The man is chaotic. The notion that a Boris administration will, as his website promises every few lines, subject London's finances and procedures to the most rigorous of scrutinies, is beyond parody. I was discussing this problem with a Conservative commentator the other day. His slightly apologetic view was that Boris might be able to surround himself with a good team, who would compensate for his rather obvious lack of qualifications. Then he looked up, caught my expression, and laughed. It was a capital joke.

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