It's a cracking show - so don't let anyone spoil it

The French couple, in their early twenties, were new to London. He had quickly found a job in media design, she in jewellery. Wouldn't Paris have been the obvious target for their talents? I wondered. "But London's so exciting," they exclaimed and there, in an adjective, lies living proof of a momentous cultural revolution.

The number of French people living in London today make it the world's eighth largest French city. Nicolas Sarkozy, on the election trail, called it "one of the greatest French cities"; his finance minister, Christine Lagarde, admitted last week that Paris has much to learn.

Poland's election result this weekend will be determined in London, where more than half a million voters live and work. More young Germans now live in London than in Leipzig. Our top colleges are crammed with students from the Asian tiger economies.

London has, over the past half-decade, become a magnet for the world's twentysomethings, not because it is cheap to live or easy to get about, but because it represents the richest, most diverse cultural scene to be found anywhere on earth. Not since the Swinging Sixties has London been so much the place to be for the young and creatively minded.

The evidence will confront new arrivals before they leave the new Eurostar terminal at St Pancras. Next door, the British Library, which has just closed its Sacred exhibition after record attendances, is putting up a competition for avant-garde designs to present in its shop window. Three bus stops up the Marylebone Road, at Regent's Park, Russians were the first big buyers yesterday at the Frieze Art Fair, which has become a fixture in the calendar of every leading gallery and serious collector thanks, in the main, to the vitality of contemporary British art.

In Bloomsbury, the British Museum has decided from next week to stay open until 9.30 most nights in order to accommodate the torrent of visitors to its unique display of China's terracotta warriors. More than a third of a million people bought tickets in the opening month, half of them from abroad.

Around the corner, the Royal Opera completed a sold-out cycle of Wagner's Ring, contentiously designed yet raved over in all quarters for the quality of performance.

Theatres in the West End, for all their dependence on pop musicals, are setting a new box-office record, 14 percent up year on year. The hottest choreographers are now resident in London and the Royal Festival Hall has been expensively restored to something rather better than its former glory.

Tate Modern has posted its highest attendances, 5.2 million in 2006, with a claim to be the most popular free museum on earth. Its crack in the floor is certainly the most talked-about art installation of the moment, an unmissable comment by Doris Salcedo on divisions in society and within the individual psyche. No art form has missed out on revival. Even humble pottery has become hot, hot, hot through the high-profile cross-dressing appearances of Turnerwinner Grayson Perry.

Cuts in state funding that might have threatened the boom were averted this week by a par-inflation settlement. And then, to cap the city's cultural confidence, Doris Lessing, who has walked much of her adult life in Regent's Park and set her novels in north London, was awarded the Nobel Prize for Literature.

Can there be any doubt that London is now the world's capital of culture? Renaissances, however, do not come about by accident. Nor do they last for ever, and there are disturbing signs that the resurgence may be in jeopardy.

The conditions for renewal were created by two enlightened acts of government. Triennial arts funding which replaced annual grants at the turn of the century encouraged directors to take medium-term risks, while free entry to museums enacted in 2002 challenged curators to show that they could sustain mass interest. In less than a year, the climate changed from cautious to creative and a mandate was seized upon to present art that would differ provocatively from trash television and formula-driven movies.

The public responded en masse. More people now visit museums than professional football matches and the average age is on the young side of 30. While there is no official statistical correlation between London's cultural rejuvenation and its increased international population, the anecdotal evidence is forthcoming from almost any newcomer you care to ask. Why London? "Because it buzzes," they reply in a bewildering cornucopia of baccalaureate accents.

Beyond the public institutions, fringe music venues, theatres and dance houses feed a continuing creativity. The Roundhouse at Camden Town has made itself a nexus of popular culture and street culture the BBC's Electric Proms next week will tune up to the background chat of school dropouts making their own music and videos on the floor below.

Diversity is all. Only in London will you find rappers working with symphony orchestras, visionary painters with elephant dung.

Financial confidence and free access apart, the single factor that has pushed London fastest to world leadership is chaotic non-coordination the stubborn insistence of artistic minds to do their own thing, irrespective of what anyone else is doing.

Yet just when confidence has reached a healthy plateau, along comes an Olympic-sized cloud. The London Organising Committee for the Olympic Games Locog for short, though nothing else about it is shortwinded is demanding a role in all cultural plans for the year 2012. Locog hires bureaucrats by the suitload and these high-paid officials are pestering creative directors with demands for targets and conformity. The chief pesterer is named Keith Khan and the mere mention of his name can drain blood from the cheeks of the cheeriest curator.

If Locog has its way, all arts in London will flourish ethnic colours in 2012 at an elementary content level. Creative choice has been harnessed to an Olympic chariot.

Creative time is being wasted on endless meetings. Creative futures are blurred with uncertainty. Locog is putting a choker on London's arts. Unless the Olympic dogs are called off, the cultural boom will end and London will revert to insular mediocrity, much as it did when the luminous 1960s gave way to 1970s stagnation.

It doesn't have to happen. With a Gospel chorus on Tuesday at the South Bank and Ramadan Nights at the Barbican, London's arts are an open church that needs no extra doctrine from the cardinals of social equality. Too much programming will kill the golden goose. If Locog can be made to leave well alone, London will give the world a cultural Olympics the like of which it has never seen in modern times.