Leader: The battle for London will define British politics

Until recently, it was hard to find anyone who didn't believe that Boris Johnson would win a second term as Mayor of London. Even senior Labour figures privately concluded that Ken Livingstone was facing defeat. But this consensus was always unwarranted. London, where Labour outpolled the Conservatives at the last general election, continues to lean left and being the incumbent is likely to harm Mr Johnson at least as much as it helps him. So the recent polls that gave Mr Livingstone a narrow lead over his rival should have come as no surprise. The air of inevitability around Mr Johnson's candidacy was always illusory.

In their respective exclusive interviews with our associate editor, Jemima Khan, starting on page 22 (and our latest scoop), both men are keen to avoid the appearance of complacency. Mr Livingstone, who fatally underestimated Mr Johnson in 2008, concedes that his Conservative opponent has "real ability, real intelligence", while Mr Johnson concedes that he appears out of touch to voters and that his description of his £250,000-a-year Daily Telegraph salary as "chicken feed" was "very stupid". In these austere times, he can no longer afford such flippancy.

The last mayoral election took place at a time when it would have seemed unthinkable for bankers to lose their knighthoods or their bonuses. One indication of how much has changed since then was that Mr Johnson, hitherto a redoubtable defender of the City, felt compelled to join the criticism of the £1m bonus of the Royal Bank of Scotland chief executive, Stephen Hester, branding it "absolutely bewildering". Voters who thought little of such extravagant rewards when their own pay was rising are no longer so forgiving.

Since the crash, Mr Livingstone has revived some of the old-left rhetoric that made him equally celebrated and loathed as head of the Greater London Council in the 1980s. But his stance on the City remains nuanced. Unlike some on the left, he acknowledges: "The Chancellor has to make a decision about what's the most you can squeeze out of these people before they bugger off." To the charge that he was too close
to the City during his time in office, he replies: "Well, I didn't have any powers to be tougher on bankers - I was the mayor of London." Yet it was Mr Livingstone who lobbied against Alistair Darling's plan to impose a £30,000 levy on non-domiciled foreigners. Like Gordon Brown, he viewed the City as a cash cow to fund social democratic objectives.

But the Labour candidate has learned important lessons since his defeat in 2008. After struggling to win support in outer London last time, he has targeted voters in this area with his impressive "fairer fares" campaign, a local version of the "squeezed middle" strategy pursued by Ed Miliband
at a national level. His pledge to freeze or cut executive pay at City Hall will also resonate at a time when real incomes are falling and London unemployment is 9.9 per cent, well above the national average of 8.4 per cent.

Both Mr Johnson and Mr Livingstone are mavericks who relish disagreement with their national parties. But David Cameron and Mr Miliband have every interest in seeing their respective candidates triumph. Victory for Mr Johnson would be a grave blow to Mr Miliband, who has already seen his party lose heavily in Scotland and struggle to open a sustained poll lead over the Conservatives. Defeat for Mr Johnson would be no less problematic for Mr Cameron, whose failed economic policies would be held partly responsible and whose own electoral prospects would be thrown into doubt. As for Mr Livingstone, a third remarkable comeback would confirm his status as the most successful left-wing politician of his generation.