Andy Crowther used to have time to play a lot of computer games. Not any more. At 33, he is now a supermarket manager in North London and has a girlfriend.

Despite the intrusion of real life, Mr Crowther still enjoys slaughtering hordes of monsters and capturing treasure in online games such as World of Warcraft and Star Wars Galaxies. But, like increasing numbers of gamers, he no longer has endless hours to earn the “virtual gold” needed to buy weapons and upgrades which make the game more fun. Luckily for him, 400,000 geeks, mostly in East Asia, are available for hire at the click of a button.

Packed into rooms and sleeping two to a mat, Chinese or Vietnamese “gold farmers” spend up to 14 hours a day in front of their computer screens, immersed in complex three-dimensional virtual worlds known as massively multiplayer online games (MMOGs).

They are “employed” by the four million people who buy gold online, including hundreds of thousands in Britain. By defeating enemies and completing mundane quests over and over again, the gold farmers' characters amass virtual gold that can then be sold online - for real money - to Westerners with better things to do.

The practice is not new. But the scale of it has mushroomed into a business worth £400 million a year, according to research from Manchester University released this week.

With an estimated 20 million paying users, MMOGs form one of the fastest growing areas of the internet. Millions of devotees take part in activities such as Everquest, Second Life and Age of Conan around the clock. They team up to fight monsters and each other, acquire treasure or simply hang out in nightclubs and coffee bars.

But to succeed in the game, a player needs money for equipment. Around £10 will buy enough for a decent sword in World of Warcraft. But a fully fledged, Level 80 character in Age of Conan, one of the newest MMOGs, can cost up to £300 on eBay.

Buying gold online is not illegal but it breaches the game companies' terms and conditions. Players who are caught risk having their accounts cancelled and their characters eliminated.

Mr Crowther, known in the gaming community as McBain, spent £25 on gold from a Chinese website last month that he then used to buy a virtual horse. “If I hadn't have bought the gold I would have had to play for months to earn enough for a mount,” he said. “World of Warcraft takes too long if you play it by yourself. I'm not a student any more. I don't have time to spend eight or nine hours a day online. If I can afford to take a shortcut then why not?”

Lee Baker, 33, an IT manager from Watford, also refused to spend months building up his World of Warcraft account. “Most multiplayer games force you to complete the same action over and over again,” he said. “You might be sent on a quest which takes 20 minutes to get to. That's 20 minutes of your life holding down one button, running around. A lot of us can't be bothered to do that.

“Buying gold means you can get whatever equipment you want. It leaves you free to enjoy the game.” Mr Baker, known in the gaming world as Lestat, said that his friends who disagreed with gold farming usually did not have jobs. “This one guy is really passionately against it,” he said. “But he plays games from 8am until 3am. I can't and wouldn't want to do that.”

Mr Baker recently paid £39.99 to a Chinese-based gold-farming site for 5,000 gold pieces that he then spent on his World of Warcraft character. “With that I could buy whatever I wanted. If I had done it properly, I would have had to complete twenty-five quests a day for ten days. Why spend that much time playing the game when you can spend a bit of cash and get past that?”

The temptation to buy gold grows as gamers progress on their virtual quests - more complex characters require more money to maintain. “You have to feed your horse, look after your armour, things like that,” Mr Baker said.

Professor Richard Heeks, who wrote the Manchester University report, said that gold farming had started off as a cottage industry but is now an economic sector “comparable in size to the Indian software industry”. He said: “In one Chinese town so many people were employed as gold farmers that they renamed it Heaven of Legend after the online game Legend of Mir,” he said.

He dismissed criticism that Chinese gold farmers were living in sweatshop conditions. “Fine, it's not a five-star hotel. But they're paid £77 a month, which is higher than the average wage, and they're given a place to sleep and fed. By Western standards it's not much but gold farming is benefiting a lot of people.”

Steven David, chief of the game security firm Secure Play, said that gold farming had burgeoned in size. “When you get people with more money than time and people with more time than money the two will find a way to meet,” he said.

Gold farmers caught practising their trade online have often suffered abuse from irate Western players who consider the practice to be cheating. One told Professor Hicks: “They treat me bad ...They keep calling me farmer, China dog and such. They non-stop racist me.”

But for others, the virtual world offers an escape from their impoverished lives. Ge Jin, a PhD student at the University of California who filmed scenes from a Chinese gold farm in 2006, said: “Their virtual lives give them access to power, status and wealth which they can hardly imagine in real life.”

Not all gold farming is located in East Asia. One anonymous farmer, based in America, wrote on his blog that his first tax return for 2001 showed $150,623.78 after expenses. Seven years later “the business was approaching $800,00 [£440,000] a year in income with hardly any costs associated with it.”

Gold farming is proving so lucrative that criminal gangs are increasingly cashing in on it. Hundreds of fake sites purporting to sell gold for the major online games have sprung up, taking money from players and not handing over the gold.

But for thousands of British gamers who refuse to dedicate their lives to their computers, the chance to play as a Level 80 Warlock has proved too much to resist.

VIRTUAL GAMES - REAL STAKES

— The real dollars spent playing the game EverQuest would make it the 77th richest nation

— A 22-year-old Australian paid nearly £14,000 for a virtual island in the game Project Entropia

— World of Warcraft is the largest massively multiplayer online game, with more than tenmillion subscribers

— A baby reportedly suffocated in South Korea while her parents played World of Warcraft in a local café

Explore Tech & Web

• Personal Tech

• The Web

• Gadgets & Gaming

Times recommends

• Point-and-go computers consign mouse to history
• YoYotech Fi7epower: the world's fastest PC
• Bridging the gap between mind and machine