He's 'a mayor for the good times'. But that didn't help the capital's top politician deal with last year's riots, and critics say he's achieved little beyond boosting his own profile. With the elections looming, we assess Boris's first term

In the introduction to Sonia Purnell's boisterous, widely praised, otherwise comprehensive 2011 biography of Boris Johnson, there is one telling omission. Over nine pages she covers his hairstyle, family history and sexual infidelities; his slipperiness, dislike of confrontation and love of money; his theatricality, his heroes Winston Churchill and Benjamin Disraeli, and even his prospects of becoming a prime minister to match them. Yet nowhere does she mention a single Johnson policy from his current job, for which he will seek re-election on 3 May: mayor of London.

As governor of Britain and Europe's largest and most powerful city – many would say too powerful – Johnson has the biggest personal mandate of any British politician. He was elected in 2008 with 43% of first-preference votes: strikingly more, in a usually Labour-supporting city, than the 36% eked out by his party at the 2010 general election under his increasingly obvious rival David Cameron.

Johnson campaigned for the mayoralty with big, if airy, promises. In his manifesto and interviews, he undertook to "work flat-out" to make the often polluted, poker-faced and disorderly capital "the greenest city in the world"; to "make our streets safer"; to combat the city's "massive increase in incivility"; to "get Londoners moving" through a no-strike deal with the militant tube unions; in short, to "put the smile back on London's face".

Things have not quite worked out like that. Since Johnson's election, the city has endured its worst riots for 30 years. Its economy has experienced its most protracted period of low growth for at least as long. There have been more tube strikes than in both the mayoral terms combined of Johnson's predecessor, Ken Livingstone. And last year the city suffered its worst air pollution since 2003.

And yet, London under Johnson has not felt like a city in sharp decline. As under Livingstone, gleaming, much-needed new transport systems continue to open. New glassy towers continue to crowd the skyline. Tourists, immigrants and the international rich continue to come. Central London seems ever busier and smarter. The inner suburbs seem ever more teeming with restaurants, artists, revived public spaces and young entrepreneurs. Especially compared with the rest of Britain, in London it often feels as if the energy and swagger and hubris of the Blair era live on. The fading, depopulating city that existed from the second world war until the 90s seems long gone.

The ambiguous condition of the capital is reflected in the opinion polls. After years of comfortable Johnson leads, they now put him just behind or just ahead of Livingstone. How responsible is Johnson, exactly, for London's mixed fortunes since he took office? And when he returns to national politics – which, if he loses the mayoral election, could effectively be in weeks – what does his record in London suggest may lie in store for the rest of the country?

Because central government has for centuries been anxious about London's potential political clout, the mayor has limited powers, mainly confined to policing, transport and planning. "There is no mayoral car, chain of office or official accommodation," Purnell writes. In his office near the top of the modestly sized, slightly airless goldfish bowl of City Hall, Johnson inherited a small staff by Whitehall standards, fewer than 800-strong, "a set of cheap-looking office furniture, venetian blinds and a phone."

David Cameron and Boris Johnson at a London Olympics 'One year to go' ceremony in 2011. Photograph: Simon Webster/Rex Features

Before 2000 London did not have an elected mayor at all. Livingstone was the first. A native Londoner and London obsessive, who had already been the potent head of the Greater London Council (GLC) in the 80s, he exploited his narrow powers to the full, while always seeking to widen them. The results were considerable, including the congestion charge, the cashless Oyster payment system for public transport, and winning the 2012 Olympics bid.

Johnson, born in New York, never previously a London politician, has followed a different path. Three weeks into his mayoralty, he took a holiday in Turkey. Ever since, he has kept up his many extracurricular interests: sniping at Cameron, over issues from the number of police officers (too low in Johnson's view) to the 50% rate of income tax (which he thinks is too high); clowning on TV programmes such as Top Gear; and writing popular history books and a weekly Daily Telegraph column for which he is paid £250,000 a year, a sum he described in 2009 as "chicken feed", and of which he loudly gives a portion to charity.

Last year, Johnson told the Sunday Telegraph his favourite politician was Ronald Reagan. The telegenic, low-effort, professionally sunny American president had an appeal far beyond his party's usual rightwing voters. For his first months as mayor, like Reagan, Johnson seemed less interested in running things than setting a mood. "Bubbles in the champagne", Purnell records, was one metaphor his aides used for his desired role as a largely symbolic "chairman mayor". While Livingstone concentrated power in himself and a tight circle of old allies, Johnson delegated, to figures his administration recruited from business and London Tory councils such as Westminster.

Initially, it appeared a clever strategy. The press – then as now, mostly ready to give Johnson the benefit of the doubt – reported a new inclusive atmosphere at City Hall. Questions that had occasionally unsettled his campaign about whether, as a part-time politician with a limited appetite for detail and a short attention span, he was competent to oversee London, were neatly sidestepped. "Boris took office with virtually no expectations," says Tony Travers of the London School of Economics, the leading expert on the capital's governance. "That was a huge advantage."

Without a concrete vision for London, Johnson's administration concentrated initially on getting rid of things. Bendy buses, the western extension of the congestion charging zone, a 50% target for affordable housing, a plan to pedestrianise Parliament Square, a proposed £25 congestion charge for the most polluting cars, the mayor's official newspaper and PR sheet the Londoner – the grand schemes or follies of the later Livingstone years, depending on your perspective, were rapidly dismantled. Another fixture of Labour-run London, the relatively liberal head of the Metropolitan police Sir Ian Blair, was forced out. The consumption of alcohol was banned on public transport: an odd move, it seemed, for a supposedly hedonistic, libertarian sort of Tory mayor. But Johnson, Purnell reveals, does not drink much himself; for all his disarming messiness, a part of him likes to stay in control.

His cuts were in tune with the abrupt national mood switch from profligacy to austerity in 2008, and prefigured what his party would do in government. And like the coalition's cuts, while they were justified with neutral-sounding rhetoric about reducing waste, they were in fact shrewdly, even brutally, political. Johnson had won the mayoralty by just under 150,000 first-preference votes, but his success had relied heavily on the peripheral suburbs: his majority was 81,000 in the constituency of Bexley and Bromley alone. "Boris is an outer London phenomenon, and people in outer London are still quite dominated by their cars," says the transport writer Christian Wolmar. Johnson's pro-motorist policies have rewarded them. Meanwhile, his less palatable public transport policies, such as a 50% increase in bus fares since 2008, have most affected the poor and residents of the inner suburbs with fewest tube stations – London's heaviest bus users and most stubborn Labour supporters.

At other times, Johnson has been less deft. During 2008 and 2009, his delegating approach almost descended into chaos. Turf wars in City Hall, personal scandals, and a sense of directionlessness prompted a rapid succession of resignations. He lost three deputy mayors, Tim Parker, Ray Lewis and Ian Clement; his chief political adviser, James McGrath; and his Olympic representative, David Ross. Another deputy mayor, Simon Milton, died last year.

"Boris does find conflict and difficult situations much trickier than when things are going swimmingly," says Travers. As mayor and GLC head, Livingstone was the opposite. Yet in an important, largely unremarked way, mayor Johnson has increasingly come to resemble his predecessor. Since his first, fumbling months, he has stabilised his mayoralty by retaining and implementing large parts of Livingstone's blueprint for London.

A public cycle-hire scheme, like the already iconic "Boris bikes" without the cute alliteration, was being planned by the Livingstone administration almost a year before Johnson was elected. Cycling "superhighways", another eye-catching Johnson policy, were also first devised by Livingstone. Transport for London (TfL), the city's powerful public transport bureaucracy, remains full of senior Livingstone appointees. The London Living Wage, a higher minimum wage to reflect the capital's costliness, has been supported by Johnson to the surprise and delight of some commentators; it was advocated to less acclaim by Livingstone.

Boris Johnson and one of his new Routemaster buses. Photograph: Peter Macdiarmid/Getty Images

Johnson also gained a rich inheritance of just-finished or ongoing public-sector building projects: Crossrail, Thameslink, the new Eurostar terminal at St Pancras, the refurbishment of the tube, the North London line and most of the city's main railway stations, the extension of the East London line and Docklands Light Railway, and, above all, the Olympics. "In some ways, Boris's policies are Ken-lite," says Travers. "Boris, luckily for him, has ended up cutting the ribbons. But he has also reasonably defended the vast public transport system in London. The bus and tube system haven't had any closures due to public sector austerity. New York has had subway lines and bus routes cut."

Johnson has helped sustain London's lingering sense of expansiveness with schemes of his own. With his flair for the visual and for the loaded political gesture, in 2008 he launched a public competition to design a modernised version of the legendary but increasingly impractical Routemaster bus, which Livingstone had removed from service. It started running on Monday. In 2008 Johnson also launched a project to create 2012 new "growing spaces" for food by this year, aligning himself with the vogue for allotments and local produce.

The latter programme is a little behind schedule: according to its website, 1,593 spaces have been established so far, and the deadline has slipped to "the end of 2012". A more serious charge is that Johnson's pet projects are luxuries rather than essentials. Wolmar calls the new Routemaster "a bit of a vanity": thanks to expenditure on development, delays, and salaries for its conductors, the tiny initial fleet of eight has cost more than £1m a bus.

Boris Johnson is confronted during a visit to Peckham a week after the riots. Photograph: Ray Tang/Rex Features

Similarly, "Boris bikes" are proving an expensive way to increase cycling. Over its first five years, the scheme is expected to cost £140m, of which sponsors Barclays Bank, despite having their company colours all over the hardware, are contributing less than a fifth. Income from rental of the bikes, even in the novelty phase of the first three months, was the equivalent of little more than £1m a year, according to Purnell. Finally, because the scheme is based in wealthy central London, which already has plentiful public transport, the bikes have had a narrow social impact: TfL says that regular users are "typically white men aged between 25 and 44, with a higher than average household income".

Johnson has not done as much for Londoners less like himself. In 2010 he defended the capital's housing benefit claimants against the "Kosovo-style ethnic cleansing" that he said could result from the coalition's cuts. But the courage of his stance was undermined by his sly knack for saying something outrageous – the "Kosovo" charge may have done more damage to Cameron's claim to be caring than any other anti-cuts soundbite so far – and then semi-retracting it. He quickly claimed he had been taken out of context.

A few months later, his limited grasp on London's social tensions was graphically exposed. In the months before the 2011 riots, "things were hotting up," says Simon Woolley, director of the well-connected ethnic minority lobby group Operation Black Vote. "One of the contributory factors was a breakdown in police-community relations." Unlike Livingstone, who had advisers who "acutely understood race inequality" and the effect it could have on policing, Johnson "has not made anti-racism a priority", according to Woolley. He cites the cancellation of Livingstone's anti-racism music festival Rise; a lack of ethnic minority workers on the Olympic site; and "well-meant but far too gimmicky" Johnson projects such as one for mentoring black boys, which has been dogged by allegations of incompetence and cronyism. "Black people warm to Boris's personality, his maverick status – I've seen him mobbed," says Woolley. "But they feel bitterly let down."

When the 2011 riots started, Johnson was on holiday in a remote part of Canada. For two days, he refused to come back. "I think the police are doing a very, very good job," he said, although the contrary was increasingly obvious. "My thoughts are very much with everybody who has suffered damage." When he finally returned, he did a walkabout in a ransacked part of south London, but his appearance in public failed to work its usual magic. "Why are you here now?" said a voice from the stony-faced crowd. "Three days too late," said another. Squinting uncomfortably in the sunlight, Johnson made a short, stumbling speech, full of perfunctory phrases and lacking either his usual zip or the necessary gravitas. Then he abruptly turned his back on the crowd and walked off, pausing only to wave vaguely at diners through the window of a restaurant.

"The riots encapsulated a nasty and out-of-control part of London's character," says Travers. "Boris is less at home in that world. He is a mayor for the good times."

Last year he told this paper, "What's so joyful about being mayor [is] that there are days you can do things that people like and enjoy. When I see the bicycles flowing around, I have a deep ... sense of creativity." This desire both to be loved and to play god is a necessary trait of big-city mayors. Livingstone had it; Johnson expresses it more openly, together with a wide-eyed wonder at London that seems simultaneously naive, endearing and calculated. On 3 May, London, often a city of crazes and bluffing and image, may, just, opt again for Johnson's child-like enthusiasm and shameless contradictions – the bicycling mayor who ran up £4,698 in taxi expenses in his first year – over Livingstone's more grownup and streetwise style of governance.

Yet truly significant rulers of cities, however many terms they serve, also leave a legacy. Sometimes it is national: in the 70s, Tory GLC leader Horace Cutler pioneered council-house sales and helped prepare the way for Thatcherism. Johnson's mayoralty, by contrast, has "not become the laboratory for Conservative policy many expected", writes Purnell. Nor has his relative popularity boosted his party more widely. The Tories did poorly in London in the 2010 general election and, mayoral polls aside, remain far behind Labour in the capital. Johnson's sole, permanent political priority, some Tories complain, is Johnson.

Unlike Livingstone, "he won't be seen as someone who profoundly changed the city", says Travers. Governing in a perpetual present, of walkabouts and witty phrase-making and overnight cramming for important meetings, eyes possibly on the greater prize of becoming PM, he has not, so far at least, shown the patience needed to reshape a stubborn, politically labyrinthine city. Even his Thames estuary airport scheme, "Boris Island", seems more of an attention-seeking sketch than a worked-through policy. Johnson, it is not widely known, has naturally tidy hair, and messes it up for the cameras – evidence of his shrewd and shameless play-acting, but also of ephemerality: even his unruly thatch doesn't last.

Travers suggests Johnson's one enduring contribution to London may be double-edged. "You can well imagine in a hundred years' time, people still talking about Boris bikes, just like people still talk about Belisha beacons," introduced to pedestrian crossings in the 30s by the transport minister Leslie Hoare-Belisha, and still in use today. "But like Belisha, no one will remember who Boris was."