If you thought concubines had been consigned to history in China, think again. Bars in the country's booming cities are now full of aspiring 'ernai' out to bag a filthy-rich businessman. Sally Howard speaks to some of those who've made it, and some who rather wish they hadn't

Falling out of bed at 1pm, 23-year-old Little Snow - concubine to a 60-year-old Hong Kong businessman - shakes off her champagne hangover, pulls on her Louboutins and begins another typical day: a boozy lunch with the girls, a visit to the sauna, shopping, speeding down the Shenzhen city streets in her midnight-black BMW Z3. For Little Snow - a translation of her name Xiao Xue - and her girlfriends luxury is the norm. 'The only luxury I can't afford,' she tells me later, recumbent on a lip-shaped sofa in one of the exclusive karaoke bars where the super-rich entertain their mistresses, 'is love.'

Little Snow considers herself lucky. Among the hundreds of thousands of young women drawn from China's provinces to the southern city of Shenzhen each year, she's achieved the ambition of many in becoming an ernai, or 'second wife', to one of the businessmen whose yuan-padded wallets have turned this skyscraper metropolis into a pleasure playground.

The girls' prey are China's nouveaux riches. Drunk on liberation after the joyless Mao years of their youth, these are men who see it as their professional and personal responsibility to dress the part and live the dream: teeing off on the improbably green greens of China's new golf clubs, crowding their wardrobes with labels such as Dunhill and Armani, and - the status symbol nonpareil - running one, or several, glamorous ernai.

'Thirty years ago it would have been a serious offence to keep a concubine,' explains Lijia Zhang, a Beijing-based feminist commentator and novelist. 'During the Cultural Revolution life was about survival rather than fun, no visiting bars or chasing girls. But the return of ernai shows how many Chinese habits, deeply culturally rooted, die hard.'

The Chinese custom of keeping concubines, or gui fei, dates back two millennia. At the height of the Qing dynasty (1644-1911) the halls of the Forbidden City in the centre of Beijing echoed with the chatter of the emperor's 20,000 concubines. According to Daoist theory, a school of ancient Chinese philosophy, as the ultimate expression of manly 'yang' the emperor was obliged to sleep with as many women as possible, the repositories of the polar force of 'yin'.

Throughout six decades of communism, however, the practice of keeping concubines was outlawed, decreed symptomatic of the bourgeois evils of imperial China that the Cultural Revolution sought to eradicate. It's a party line that escaped Chairman Mao Tse-tung, who - according to reports that emerged after his death - ran a secret harem of 20 peasant women well into his dotage. President Jiang Zemin (1993-2003) exuberantly embraced this hypocrisy, keeping several women - including a prominent Chinese soprano - as secret ernai during his years in office.

Yet there's nothing sotto voce about the 21st-century spin on ernai culture. In the lexicon of the moneyed businessmen who collect concubines as they do cufflinks, their girls are 'golden canaries' who, like spoilt pets, are holed away in lavish love nests, pampered and taken out for the pleasure of their masters. Little Snow's remuneration is typical of Shenzhen ernai: rental on a fashionable penthouse in one of the city's dazzling white apartment blocks, plus a 5,000-yuan (about £350) monthly budget for clothing, haircare and skin-whitening treatments. That's more than double China's average monthly income.

In turn her 'husband' - a successful industrialist whose factories stud mainland China - entertains Little Snow once or twice a month. The nights are raucous, but the sex lacklustre, to Little Snow 'a function no different from brushing my hair or drinking a glass of water'. He's up before the sun rises, sometimes leaving a rose on the pillow.

Such romantic impulses are, however, lost on Little Snow, who prefers talk of lucre to love. 'It's in my interest to please him, to make myself favoured. One of my husband's other ernai [she's aware of two others], in Shanghai, had a house bought for her, and that makes me really mad. After all, this isn't for ever. I've seen the girls who are ernai until they're in their early thirties and their husbands [she uses the term without irony] leave them with no ceremony, nothing in the bank… no work, nothing.' Do ernai in her circle share this unblinking focus on financial reward? 'Some girls do fall for their husbands, but that's trouble. If you're abandoned with a child, you're stupid.'

However glacial this affair with the man she derides in bleak moods as her 'puppet-master', Little Snow couldn't conceive of taking a younger boyfriend on the side, as many ernai do. 'My mother lived through very dark times, and throughout my childhood she told me: "Marry well, marry rich." Many of my generation experienced the same pressure, even more so the only children [as farmers, Little Snow's family escaped the one-child policy]. I'm a simple girl from the provinces and I couldn't find a rich man as a husband, so the next best thing was to become an ernai. I'd never lose face by chasing "love" and having a boyfriend who couldn't buy me an expensive handbag.'

Shenzhen's party girls are merely the outward face of a fashion for keeping concubines that extends across China's moneyed and middle classes. Bai Chun, a Beijing-based lawyer, has seen its dark side. The go-to man for comment when ernai scandals make national news, Chun has become an unofficial campaigner for wronged ernai - girls who have been duped into becoming wives with a specious promise of future payment, girls disposed of when their youthful lustre begins to fade, or abandoned with an illegitimate child who can't be registered with the authorities (and is therefore a 'non person' with little hope of a good future).

'The worst stories I hear are of gullible educated girls who become ernai very young, often at university,' he tells me. 'They're much more susceptible, somehow, to being flattered into falling in love.'

President Jiang, it seems, wasn't the only powerful Chinese man with an appetite for accomplished young women. 'Students at Beijing's Academy of Music are always favourites as concubines to politicians,' says Chun. 'For older Chinese, buying an artistic or musical ernai is like buying culture to your taste… A businessman who likes classical music will choose a violinist as his ernai, for example.' And there's no shortage of young women willing to take them up on the offer. Landing what's referred to in slang as a tai tai, or rich older man, is the fixed aim of many Chinese university students, some of whom subscribe to the popular Chinese saying 'It is better for a woman to marry a rich man than for her to have a good job.'

Indeed, so prevalent is the older male/younger student dynamic that in Guangzhou, a prosperous city near Shenzhen, a university recently felt compelled to issue written warnings to female undergraduates highlighting the 'moral impropriety' of having affairs with older men. Despite the homogenising impulses of communism, China is a country stratified according to class and gender, and - for some students - becoming an ernai is a shortcut to rubbing shoulders with China's political powerbrokers.

'There have certainly been cases of political men setting their ernai up in business and introducing them to the right people in power,' says Chun. 'So you can see how this would tempt an ambitious young girl.'

A girl such as Cai, now a 30-year-old doctor from the grasslands of Mongolia, who is one of Chun's clients. At 25 she became ernai to her 78-year-old lecturer, who supported her through medical school, then lost interest as she approached her thirties, abruptly withdrawing his finances and affections.

'I now know,' she says sourly, tearing at a tissue in her lap, 'that he wanted me because I was to his taste - a pure Mongolian girl. He's a healthy man for his age: he doesn't smoke or drink and his preference is for virgin ernai. But I was naive; I fell in love with him… in my way.' Chun interjects, 'Seventy-eight and more virile than a 20-year-old, she tells me - incredible! Ernai have never worked so hard as after Viagra! Ha!' Cai, who has not had a boyfriend since her professor, glumly asserts that she will never trust men enough to find love.

What does Chun hope he can do for Cai? 'It's a struggle. Even when an ernai and "husband" have a contract drawn up [a nascent trend in Shanghai but rare elsewhere] the courts rarely find in her favour. The process of the Chinese courts is antiquated, judging the girls by daode [in rough translation the "system of morality"], rather than objectivity, or even contractual law.'

So, although Chun takes on up to 10 new cases per month, his successes are few. 'My last case is typical. I represented an ernai who had been given 80,000 yuan [about £6,000] over a three-year relationship with her husband, and had had a child with him,' he says. 'She petitioned for ongoing support for the child, but the court ordered that the ernai should give the original 80,000 yuan back to the man's first wife. Understandably, the ernai is destroyed.'

If the response of the Chinese courts is routinely unflinching, that of first wives is less predictable. On the one hand, the mistress boom is contributing to a surge in divorces, and detective agencies in Shanghai and Beijing report a brisk trade in first wives seeking proof of their husbands' ernai. Debang, an agency set up in 2006 by a group of divorced women in Chengdu, specialises in catching husbands in flagrante with their ernai (and making husbands pay dearly for any indiscretions) and has recently expanded into several cities.

Disenfranchised first wives are, however, but part of the story, says Richard Chuang, a Shanghai businessman I meet in Sanlitun Bar Street in Beijing, where the city's would-be ernai sit in miniskirted ranks, eyes scanning the bar for flush suits out for fun. Sometimes wives play an active role in seeking out concubines for their husbands' pleasure. 'I know a rich woman, and there are many like her, who's married to some big shot, lives in a huge villa on a compound outside Beijing, is bored stupid - and her hobbies are golf and finding new sex partners for her husband. She sees it as her job to maintain diversity in her husband's sex life and is unapologetic about it.'

To a China perfecting its steps for its waltz on the world stage, its politicians' thirst for ernai is discomfiting. Not wanting to risk their meal ticket, the unwritten code of most ernai is secrecy; but, when they do talk, the effect can be explosive. Over the past couple of years, in a rash of salaciously reported cases, ernai have brought down their corrupt communist official 'husbands' - most notoriously Pang Jiayu, the former deputy head of the provincial political advisory body in Shaanxi province, who was expelled from the party when his 11 ernai teamed up to expose him in 2007 and whose taste for mistresses earned him the nickname 'mayor zipper'.

The scandals aren't restricted to the political domain. In 2005 a media furore was provoked when Da Beini, a Shanghai ernai, auctioned on eBay the booty gathered during her relationship with a prominent Shanghai property tycoon, including several opulent flats, a Lexus Sedan and a cache of Louis Vuitton handbags.

But behind the screaming headlines and the champagne-lubricated high living, the loveless liaisons of the booming concubine culture betray a more pertinent truth about modern-day China.

'The country has changed rapidly; but Chinese thinking hasn't caught up with this new reality,' says Yang Erche Namu, aka Namu, one-time mistress to a diplomat and now a postergirl for modern Chinese feminism, whose ballsy bestselling books urge Chinese women to pursue emotional and financial emancipation. 'Some men are getting very rich, with cash to throw around, but at the same time the wealth gap is widening and the countryside is full of young girls living in poverty. So it's natural that love becomes a transaction - it's a simple case of supply and demand.'