Amol Rajan: Beware the huge power of the not-quite-so-powerful

Modern elections can be won or lost according to what I call The Underdog Effect. All media outlets, except those who are actually a branch of a political party – like Fox News or The Sun – have an interest in seeing an extremely close contest. A nail-biting finish makes for the best story.

So the media overplay the chances of the underdog and underplay the chances of the favourite. That gives the underdog an aura of electability they don't actually deserve – but thereby increases their attractiveness to voters and so their eventual chance of winning. You're seeing this in the contest to be the Republican party's presidential candidate this autumn, which is the longest suicide march in modern American history. Mitt Romney should be clear favourite. But Newt Gingrich's superb performance in South Carolina has created a momentum which all of America's media wants to feed. Gingrich finally triumphing over Mitt the Moderate – long established as the front-runner – would be a great story.

Two remarkable polls over the last week have suggested that something similar might just happen in London's forthcoming Mayoral elections. A YouGov poll last week had Boris Johnson – long presumed likely to waltz to victory – two points behind Ken Livingstone.

Then a ComRes poll for yesterday's Evening Standard confirmed the surprise figures: Livingstone was again two points ahead. That's after being 8 per cent behind Boris in a Standard poll in November. The underdog is threatening to become the usurper. Game on! Even the Standard headline, which referred to an election fight "on a knife edge", shows how we hacks savour a close contest. Given that Boris has long been the favourite, reporters everywhere will know that the better Ken does, the bigger the upset – and the better the story. Labour campaigners ought now to put huge energy and resources behind Ken's campaign. In November I sat next to one of the failed candidates for Labour's leadership at dinner. He was so utterly hateful of Ken and dismissive of his chances that I presumed he was exceptional in the party. But in fact senior Labour figures have been briefing against Ken for weeks. If they want control of London again, that should stop.

As for Tories, the most striking finding in the poll is that Boris still leads Ken in the outer boroughs that delivered him victory last time, albeit by less. But in the inner boroughs, Ken is well ahead, with 68 per cent. Boris is doomed unless that number comes down. How to do it? The answer, in two words, is London Citizens. That will be the subject of my Thursday column.