I’m an ex-Londoner who has lived in Paris since 2002, mostly because I was able to buy a nice flat there for £60,000. Every time I return to London on the Eurostar, I feel momentarily bewildered. The first thing you see as the train pulls into St Pancras is the restored Victorian brick palace at the head of the platform, now a five-star hotel.

You walk into the Tube, which makes the Paris Metro feel decades out of date. Central London smells of money. Then there are London’s colours, which after white and grey Paris hit you hard. The bright red of the buses and postboxes is the perfect shade for the rainy climate. And whereas Paris white buildings subtly rebound the sunlight, in London all colours clash: red-brown bricks, green trees, and the flowers in the gardens. Most colourful of all are the people: in London (to borrow from the poet Jenny Joseph) you can wear purple, with a red hat that doesn’t go. You can wear whatever you like. The overall effect is of a psychedelic 1970s album cover.

This is the London that the world now sees. The city’s brand has transformed just since the 1990s. London ranks top or just behind its rival New York in a variety of reputational league tables. So what is London’s brand today? And what are the threats to it – the forces that might one day knock the city out of the front rank?

The first word that’s central to London’s brand today is money. As the branding expert Simon Anholt has noted, the cost of London is both deterrent and lure. Price adds to London’s cachet.

Money has helped convert London from a national capital into a global one. London now drains hyperambitious people from countries everywhere. The most driven young bankers, consultants, artists, graphic designers etc from Malaysia, Italy, Australia or the Netherlands no longer want to make it in their national capitals. They want to make it in London or New York, where the rewards are highest. This trend is relegating cities like Amsterdam, Milan and even Paris to national status. These cities are cosmopolitan, not parochial, but for most of the global elite they are second-tier locations. Saskia Sassen of Columbia University, a leading thinker on cities, asks: ‘Are we seeing a bunch of ‘super-places’ emerge that are really different, and that become necessary anchors for a firm or an individual or a project?’

Money has helped convert London from a national capital into a global one. London now drains hyperambitious people from countries everywhere

The second component of modern London’s brand is colour – both literal and metaphorical. The city I recall as a child and young man was a greyer place. When I started work here in 1995, tired people would wait on packed platforms for 1950s Tube trains. Coffee was a scarce and exotic drink, like nectar. Eating a meal outside was forbidden. The city centre was almost uninhabited, and closed at 11PM anyway, followed soon afterwards by the Underground. Housing was cheap because there wasn’t much money about.

But in the space of a few years in the mid-1990s, London turned into a more enjoyable, almost continental European city. That was largely because it was rapidly attached to the European continent. On 1 January, 1993 the EU legally became a single market, making it much easier for continental Europeans to move to London. In 1994 the Eurostar opened. By 1996 EasyJet and Ryanair were ferrying Europeans cheaply back and forth to London. Meanwhile the economy recovered.

London absorbed influences from cities like Paris and Barcelona. Quickly, alongside the age-old pubs, it acquired cafes with pavement tables. Licensing laws were relaxed. There was a new attention to public spaces: London built Parisian-style grands projects like the Millennium Bridge, the Tate Modern and the London Eye. People started to move back into the city centre.

The copying of good ideas from city to city has only accelerated since: for instance, London borrowed its mayoralty, give or take a few details, from New York, its bike scheme from Paris, and it’s modest shared space streets (Kensington High Street, Exhibition Road) from Copenhagen. And so London has come to be seen not just as an economic and political capital, but also as a colourful place to live. In a survey by the Boston Consulting Group and the recruiting firm The Network last year, over 203,000 mostly well-educated people in 189 countries were asked online to name up to five cities where they would ‘consider living abroad’. London came top, listed by 16% of respondents. And as the urbanist Richard Florida notes, the respondents weren’t chiefly interested in high pay. They could have got that in Dubai or Doha. ‘The top four factors,’ Florida writes, ‘were: appreciation for your work, good relationships with colleagues, good work-life balance, and good relationships with superiors.’ In other words, ambitious people want interesting jobs with stimulating colleagues in nice places. That’s London today.

Modern London’s colour is also in the skin hues of Londoners. The city isn’t a multicultural paradise, but it’s probably the closest thing on earth to one. When the French footballer Thierry Henry was at Arsenal, he said, ‘I love this open, cosmopolitan city. Whatever your race, you never feel people’s gaze on you.’ (Incidentally, Premier League football, now watched around the world, must have a major influence on the shaping of London’s brand.)

London today is a place without a dominant national culture. In Paris, French codes of etiquette still constrain all human action: start every conversation with ‘Bonjour’, don’t wear a tracksuit to go to the baker’s, etc. But in London you can not only wear purple, but dye your hair purple and then jog down your local high street. To the Paris-trained eye, half the London population looks like punks or bag ladies. Even in the City, the tie is rapidly going the way of the bowler hat.

This is freedom. To most foreigners, London now looks like a place where you can self-actualise: where you can dress and live more or less as you want without anyone bothering you. A Spanish woman I know in London, after much agonising, finally, in middle age, came out as a lesbian. The response in her London circles: mass indifference. London’s mayor, Boris Johnson – hair uncombed, speech almost uncurtailed, his sexual past licentious – incarnates the freedom that the city grants its citizens. And of course he’s rich. Johnson is part of modern London’s brand.

London’s money, colour and freedom feel very of our time. However, the city’s history remains central to its reputation. The last key component of London’s brand is stability. Britain’s ancient institutions change very slowly. The Tower, bewigged British judges and possibly even Queen Elizabeth are forever. London’s stability has attracted refugees since the French Huguenots. Now it is luring Chinese and Russian elites who are unsure where their own countries will be in ten years’ time. They see London as a safe place to stash their money and children.

The city’s global brand has been created with little conscious effort. As John Dickie of London First points out in this collection of essays, London’s promotional budget of £19 million is less than a tenth that of Singapore’s. However, London has relatively little need for professional branders. A branding campaign like ‘Glasgow’s Miles Better’ can change the image of a lesser known city, but London’s brand is created by pop culture, by word of mouth from visitors and immigrants, and by the vast London-based media. The BBC and Britain’s Guardian and Mail newspapers run some of the world’s most-visited news sites. The global 1% prefers The Economist and the FT. France, Russia, China and probably even the US wish they had that influence on planetary opinion. A consequence of this is that London is daily world news.

London’s pop culture may have an even deeper effect on the global imagination. The Olympics helped brand the city (at a cost of £9 billion), but so did the recent commercially produced children’s film Paddington, which stars the bear as the ultimate modern Londoner: a strange-looking foreigner, who feels instantly at home in the city largely because he is fluent in the global language.

The city’s de facto separation from the UK accelerated after 2008, when the rest of the country fell into the Great Recession and London just kept getting richer

The film enters a long tradition of London’s cultural imperialism. My father grew up in South Africa in the 1950s reading novels that all seemed to be set in London. He knew the place long before he ever saw it. It’s hard to think of a London branding campaign that could have a more enduring impact than, say, the Sherlock Holmes stories.

But London’s brand is vulnerable. Andrew Adonis – Londoner, Labour peer and writer – lists the city’s problems as follows ‘Housing, housing, housing.’ What’s happening in London’s housing market can no longer be described as gentrification. That was the ousting of the city’s working class and bohemians. Now, as housing prices hit new levels, many middle-class people are being forced out too. Given that the Green Belt makes expansion difficult, the solution for London may be to adopt de facto satellite cities.

When the High Speed 2 rail line opens, notes Adonis, ‘Birmingham will be half an hour from London, and Manchester and Leeds an hour. That’s hugely exciting.’ But even foreign cities like Lille, Brussels, Rotterdam and Paris are increasingly within London’s orbit. London employers may need to strike new deals with certain workers: live elsewhere, even abroad, but check in at the office once or twice a week. London will increasingly become not a home but a destination – a vast conference centre, or hotdesking space.

That trend is already quietly happening. I sometimes drop the kids off at school in Paris at 8.30AM, and later that morning meet someone for coffee near Kings Cross. More and more people relate to London like that. Encouraging ‘occasional Londoners’ will allow London companies to pay workers below the London premium, and save money on office space. It will also allow workers to school their children elsewhere. It’s true that London’s state schools have gone in the space of ten years from performing below the English average to leading the nation. However, they are still not good enough to satisfy some of the world’s most ambitious parents. If London is to persuade more families to stay, it will need more housing and better schools. Currently, says Michel Mossessian, a French architect in London, there is something of a ‘seven-year cycle’: people work seven years in London but then often leave once they have children. At one point Mossessian’s firm employed 14 nationalities; but some of them left when they reached the end of their personal cycle.

The other threat to London may come from Britain. The city’s de facto separation from the UK accelerated after 2008, when the rest of the country fell into the Great Recession and London just kept getting richer. The UK as a whole had already lost global clout due to the Iraq war, and now barely has a seat at the table in Brussels, in negotiations over Ukraine, or in the Middle East.

Yet the British government still has clout over London. Adonis notes that London’s mayor is ‘the public official with the largest electoral mandate in all of Europe except the French president.’ That is a form of soft power. However, London has very limited tax-raising powers. The big decisions on immigration, regulating the City, and whether the UK should stay in the EU will be made by Britons – quite possibly against London’s interests. Indeed, some Britons may actively want to thwart a city that increasingly has its own identity. ‘I’m not English, I’m a Londoner,’ says a character in Stephen Frears’s 1987 film Sammy and Rosie Get Laid, and that’s a much more common sentiment today. Adonis says: ‘Suspicion of the city goes hand in hand with the success of the city.’

It’s no coincidence that the heartland of the UK Independence Party is Essex, traditional refuge for the white working class driven out of London. If the next government holds a referendum on EU membership, the bookmaker Paddy Power is offering odds on that Britons will vote to leave. That would be a catastrophe for London. It’s not just that the banks might move. Imagine if every German, Italian, Spaniard etc. in London had to apply for a visa to stay. London might have to threaten Britain with economic blackmail to ensure the referendum goes the right way.

Another obvious threat is terrorism. Londoners dealt brilliantly with the 2005 attacks, refusing to isolate Muslims, but a worse attack could hurt London’s reputation for stability. Then there is the risk of renewed riots, as in 1981, 1985, 1995 and 2011 – only this time starting from even higher levels of inequality. Any violence in London will be amplified by the city’s media and travel the world, damaging the brand.

But the most likely threat to London is that it becomes a sort of mass gated community of the world’s richest people. It would be a city without young people (except heirs) and without poor people (except those who sneak in or are admitted for brief service deliveries). Then London would end up looking rather like a massive chilly Monaco – but with high taxes to support all the excluded Britons outside the gates. That wouldn’t be much fun. Perhaps one day we’ll look back on the early twenty-first century as London’s brief doomed golden age.