As economic storm clouds gather in the London sky, down below the political contest between Ken Livingstone and Boris Johnson for the city’s mayoralty is turning equally nasty. This is excellent news. Democracy and decorum never mix. A grudge match between the cheeky chappie and the Tory card is guaranteed to project London politics onto the national stage. And there is still three months to go.

Livingstone has been in office for two terms and is falling foul of the corruption of power. Longer terms are banned by constitutions the world over. Tony Blair’s ever slapdash legislators forgot this, giving Livingstone the chance still to be with us in the Olympics year.

Belaboured by police inquiries and media revelations, Livingstone last week bizarrely pleaded with the public to lay off him as London had a “presidential constitution” like in America. Accountability was due only at the next election. Until then, by implication, he is an elected dictator. Those who did not like it should blame Blair - a habit he has caught from Gordon Brown.

Livingstone is wrong. Presidential constitutions are rarely dictatorships. They customarily have supreme courts and independent legislatures, usually with control over presidential budgets. Livingstone suffers no such constraint. He was granted extraordinary power by John Prescott in 2000, when Prescott incidentally assured Londoners that a mayor would cost them just 3p a week. Livingstone is now costing the average council taxpayer £300 a year. His staff costs have inflated from £12m when he came to office to £33m today, while his publicity empire is estimated at £100m, including a mayoral newspaper.

Mayor Livingstone has become the same man as ran the Greater London council into the ground in the 1980s, except that the range of favoured cronies and clients has expanded. His luxuriantly upholstered front organisation is the London Development Agency, linked to his “race relations” ally, Lee Jasper, with a budget of some £400m apparently immune to serious scrutiny.

Millions flow from the LDA to such obscure outfits as the Rich Mix centre, the Green Badge Taxi School and Brixton Base, allegedly “safeguarding” 1,000 jobs in the capital. Many recipients are unknown to the Charity Commission or Companies House and the LDA paper trail is said to defy audit. This is government worthy of Haiti.

Meanwhile, the mayor’s aides, on public salaries of £100,000 or more, blast the ether with dirty tricks e-mails aimed at such sworn enemies as Trevor Phillips, then head of the Commission for Racial Equality, Notting Hill carnival organisers or writers for the London Evening Standard. Last week Rosemary Emodi, Jasper’s city hall right-hand woman, was caught with a friend (and recipient of LDA handouts) on a freebie to Nigeria. The two of them claimed to be investigating a mayoral plan “to bring youths of African descent from the UK . . . to reconnect with their roots” in Nigeria.

This is all pure GLC. When charged with illegally using public money for private political purposes, Livingstone chirps that his staff “work such long hours” that they have too little private time to show their love for him by safeguarding his electoral interests from home. Besides, they must accompany him, en masse, to India, Cuba and Venezuela.

Such spending is supposedly accountable to an elected London assembly, to auditors, regulators and Whitehall’s “government office for London”. None of these has even remotely done its job. The last has contrived to grow bigger since Livingstone ran London than it was when it ran the capital on its own.

The Greater London Authority Act was overseen by a minister, Nick Raynsford, who reportedly had mayoral ambitions at the time. Accordingly it opted for a “strong mayor” model and in spades. The assembly was kept small and powerless. Its one serious power, to reject the entire London budget, requires an improbable two-thirds majority. It has become the mayor’s much-abused poodle.

Meanwhile, local auditors are consumed with the top-down monitoring of central government targets. They have proved useless as a curb on inefficiency and corruption in local government (except for Shirley Porter, the Tory leader of Westminster). The Audit Commission’s green light to Livingstone’s regime at city hall is a scandal. So, too, is the Charity Commission’s tolerance of his use of Muslim organisations, supposedly charitable, openly to campaign for him. This would have them stripped of charitable status were they not “ethnically sensitive”.

So who will guard the guardians? The answer, for want of anything else, has been the press in the form of London’s one serious newspaper, the Evening Standard.

The Standard has fought a lonely but effective campaign to bring the mayor’s misdeeds to public attention. In doing so it has rendered the local global. The result of its campaign has already been four police investigations into the LDA and a possible inquiry by the Electoral Commission into Livingstone’s use of public funds for personal vendettas.

Even the Tories on the assembly have been showing signs of life. Livingstone merely accuses his tormentors of being racist or Tory or in thrall to embittered whistleblowers.

We can almost hear him saying in the tones of New York’s Tammany Hall, “and we know where they live”.

I was an enthusiast for elected mayors. More than a dozen of them have taken office in England and have proved successful, most being reelected last year. In London I must therefore swallow the Livingstone experience with a dose of salt. He began well. He ran as an independent and emerged as an undeniably popular mayor of all Londoners, unlike group leaders elsewhere, answerable only to party factions.

The speed with which Livingstone’s decisions favoured certain developer/architects was, shall we say, surprising. So, too, was his U-turn to get rid of bus conductors and in favour of skyscraper offices and luxury flats. But as he pointed out last week, no other big British city under party group control has forced policemen out of their cars onto the streets or levied a congestion charge against government opposition.

These achievements may be equivocal: the extra policemen are extras and not out of cars, while the congestion charge costs a fortune for precious little return. But Livingstone, at least in his early years, gave the leadership of the nation’s capital the stamp of legitimacy that it sorely lacked under Whitehall direct rule. Although he lost his battle with Prescott over the wasteful privatisation of London Underground, he was right to fight and was proved right in the outcome.

Direct election has refreshed politics in the capital. Still three months from the vote, its politics has become national box office. The campaign of Johnson, the jokester Tory, started as farce but is acquiring confidence and plausibility, as has that of Brian Paddick, the reticent Liberal Democrat and former police officer. Johnson is a rare Conservative both in his appeal to the young – where he is far ahead of Livingstone in the polls – and in his capacity to match his opponent’s adroit use of humour. To those who complain that his experience of office is limited he can ask if they really prefer Livingstone’s unlimited experience.

Livingstone has sacrificed any credit he might deserve for so firmly entrenching the London mayoralty by his incorrigible cronyism. He lacks any vision for the city beyond that it should be a tax haven for the rich and the Thames should be pepper-potted with ugly riverside towers. He should never have been allowed to stand for a third term. That a new law passed last year not only did so but actually gave him even more power, notably over London borough planning, is scarcely believable. The capital is in chronic need of a properly accountable assembly.

Yet while the minuses of Livingstone outweigh the pluses, the account of mayoralty as such remains in credit. It has pluralised public debate and diluted the dominance of the big party leaders. As of today, its security seems proof even against the antics of the incumbent. I would still rather have a mayor than not. But London needs a better one, desperately.

Times Recommends

• In the real world, the public sector must pay
• Playing politics in a land of double Dutch
• Be like the plinth people: not set in stone