Johann Hari: It's the policies that count – and that means Londoners should vote for Ken Livingstone

Are we becoming an Attention Deficit Democracy, where we are swayed by shiny objects and empty images rather than – crazy idea! – the policies that affect our lives? When Londoners stream into the polling booths tomorrow, they won't just be picking between Boris and Ken. They will be picking between two different ways of doing politics.

From London to Washington DC, the right is increasingly losing the argument, on everything from Iraq to global warming to the need for government regulation. They know they can't win on the issues – so they are trying to dissolve politics in an acid-bath of distracting trivia.

They are trying to make the US presidential election about whether Barack Obama wears a flag-pin, and what his pastor said one Sunday when he wasn't there. They have tried to make the London mayoral election about the 300 bendy buses on our roads (out of 6,000), Ken's purely symbolic decision to speak to a despicable but anti-al-Qa'ida Islamic cleric, and what Lee Jasper (who?) e-mailed to Kumar Murshid (who?) about how to spend 0.0000000001 per cent of the mayoral budget.

Look! It's a picture of Boris on a bike! He must be eco-friendly! Never mind that he has a bitterly green-bashing record, while it's Ken who is committed to spending £500m on new bike lanes. Look! Boris calls for a safer London! Never mind that he also whispers he will make "big savings" and "real economies" in the police budget in order to cut taxes for the rich.

Beneath this junk, there is a real election going on. Let's start with the issue discussed with hushed anxiety in every London pub: housing. It's increasingly impossible for anyone but the rich to live in London; people shriek with joy if they can find a shoebox on the edge of a sewer going for £500 a month. In this election, one mayoral candidate is committed to a big programme to help the poor and middle-class to stay here. The other is committed to a big programme to help the already-rich own more.

Ken has introduced a rule saying that if you want permission to build homes in London, half of all the stock has to be affordable to people on an average wage. And he has now – finally – been given £4bn by the government to launch the biggest home-building programme in the capital in a generation. Boris, by contrast, says Ken is "hung up" on the percentage of affordable housing – maybe it does look like a hang-up from Henley – and will ditch the rule demanding it. His plan is very different: he is committed to spending £130m on a First Step Housing Scheme to help first-time buyers. Sounds good – but look at the small print. You would need an income of £60,000 to qualify – and that rules out 80 per cent of Londoners.

In Spectator-Land, these people are the "struggling middle class" who must be the sole beneficiaries of state support. In the real London – Ken's London – they are the cosseted elite who need help less than the rest.

How about the biggest issue facing London in the long term – global warming? Half of the population of this city lives on a flood-plain – and as the sea rises, we become harder and harder to protect. The salt-water is already swelling towards us. When it was first built, the Thames Barrier had to be raised once every two years; now it is raised 20 times a year.

After New Orleans, the London Assembly studied our flood defences – which are the responsibility of Westminster, not City Hall – and found great swathes are in an "appalling" condition. The more greenhouse gases are belched out, the more likely a Katrina-on-the-Thames becomes. (Excuse me for a moment – I must go and buy a flat in Hampstead ...)

There is a bright green line between the candidates. Against the sneering of virtually all the press, Ken pioneered a hefty tool against global warming, now copied across the world: congestion charging. He has brought the number of cars in the capital crashing down by 70,000 a day, and shown that if you massively invest in buses, you can get an extra two million people on to them every day. Now he is taking it up a step by making the drivers of the most climate-destabilising cars of all – SUVs – pay £25 to enter the zone.

Boris opposes it all. He admits he "cheered" when George Bush refused to sign the Kyoto treaty, adding: "When Bush says no, he is doing what is right for the world." He will slowly peel back the congestion charge and protect SUVs. About driving these Chelsea tractors he says: "Tee hee, I said to myself ... out of my way, small car driven by ordinary person on modest income. Make way for the Nissan Murano."

I could fill this newspaper with issues where the two men are on opposite sides of the sane/barking spectrum. Boris wants "more deregulation" of the City – in the middle of a global crisis caused by extreme deregulation. He wants to reprivatise the Tube, because it worked so well with the national rail network. He compared gay marriage to bestiality. He thinks he can get Bob Crowe to agree to sign a no-strike deal. And on, and on.

But the biggest gamble if we pick Boris will be with London's febrile ethnic mix. London today is a cocktail of Chinese refugees and Latin American rickshaw drivers and African exiles; if there's anywhere on earth that could release a convincing cover-version of "We Are the World", it's us. But it's easy to forget how combustible it is.

Live in east London and you hear a simmering ethnic resentment on all sides that could easily erupt – especially as we head into an economic downturn. Only a few years ago, Paris erupted into its bonfire of the cars-and-vanities after a right-wing politician reacted to flickers of racial tension with crude language. Do we want to risk having a mayor elected by the white outer suburbs who has repeatedly called black children "piccanninies" (and not just in spoof articles), tells a black presenter "you can't out-ethnic me", and responded to the 7/7 massacres by attacking the Koran and announcing "the problem is Islam" because it is "the most viciously sectarian of all religions"?

Ken Livingstone – with his adenoidal, amphibian populism – is the most successful left-wing politician in Europe today. Born into the white working class in the rubble of post-war London, he has helped steer the transformation of this city through an amazing flourishing of sexual freedom and immigration – and faced down Margaret Thatcher and Tony Blair on the way.

At a time when most politicians cower beneath a lightning-storm of opinion polls and focus groups, he pushes politics forward in quantum leaps – on talking to the IRA, on gay equality, on the environment. Whenever he has the power to, he ploughs money into services – like buses – used by the poorest. If Londoners replace him tomorrow with the political love-child of Margaret Thatcher and Billy Bunter, we will have four long years to stop seeing the funny side.

j.hari@independent.co.uk