With a laboratory near Pudong International Airport and a factory with 65 workers three hours' drive from Shanghai, Chang's company manufactures and ships hundreds of kilograms of drugs such as mephedrone and methylenedioxypyrovalerone (MDPV) to Europe and elsewhere each week. And while some countries rush through legislation to outlaw his products, Chang and businessmen like him are one step ahead - preparing drugs that will bypass classifications and continue to offer profitable and legal teenage kicks.

Mephedrone first surfaced in 2007 and is one of a family of new designer drugs that is sold under the guise of 'plant food' and 'research chemicals'. Legislation has been rushed in to ban it in Australia, Sweden, Germany and Britain, where a number of deaths linked to use of the drug have been reported.

In a case last year in Australia, federal police seized 20kg of mephedrone and authorities said they were aware of a Hong Kong-based buy-and-sell website where Australians had left advertisements looking for the drug.

Posing as customers for buyers in Britain, we are shown around Chang's empire and see inside a sophisticated and efficient organisation that is indifferent to controversy over the effects of its drugs and driven by a single motivation: money.

Boasting that his company sends more than 100kg of MDPV, a drug that was last month banned in Britain, along with mephedrone, to the country each day, Chang makes it clear that he views the deaths of two British youngsters as a business inconvenience rather than a moral dilemma. Referring to Louis Wainwright, 18, and Nicholas Smith, 19, who died in Scunthorpe, Lincolnshire, in March, after reportedly taking mephedrone, Chang says with a sigh, 'Accidents have happened and those two young boys died in the UK. As a result, UK customs recently have been very strict and lots of packages from China and India are stopped and seized.

'It's in the media, on the TV and in the newspapers and a lot of our customers are worried. They talk to us about it. But we assure them there is no risk for them.'

The deaths prompted a tightening of customs checks on imports of chemical substances even before legislation was brought in banning mephedrone and related compounds - but Chang tells us he is able to dodge checks in Britain.

'Luckily, our packages to the UK have no problem,' he says. 'We have agents in Europe so we can send to Ireland, to Austria, to Spain and to Italy, and then the package will be resent from those countries. If [the package] comes from outside Europe, then there might be trouble. Within Europe, the UK customs normally will not check.

'If it is stopped ... we always refund or reship. That is why we have so many customers in the UK. There is no risk [for them].'

Chang's company sends its drugs to Britain by express courier, switching from one company to another depending on which runs into the least problems with customs over its packages of 'plant food'.

At the entrance to his office, barrels of MDPV are piled up alongside dozens of 1kg packages that he says contain the drug, ready to be taken to the airport.

The imaginary order we propose to him - 10kg of MPDV a month - is almost laughably small, he implies.

'It amounts to 120kg a year. I have that much in my office now,' he says. 'Every month we produce two tonnes of MDPV at our plant - 2,000kg every month. Every day we ship more than 100kg [of MDPV] to the UK. You can see the stock here in the office is ready for shipment. It is shipped very, very quickly.'

Even allowing for transshipment through a European country, packages are delivered in three to four days from the time payment is deposited in his account, he says, adding with a knowing grin: 'Some packages we send directly to the UK. We have our own methods.'

The boom in demand for legal highs in Europe has generated a huge new revenue stream for Chang's company.

'It has all happened in the past two years and the demand from the UK and other countries just keeps increasing,' he says.

Set up seven years ago, the company was already doing brisk international business, turning out five or six new generic drugs a year, ranging from antiretroviral drugs for HIV sufferers to impotence drugs. The company is flexible enough to be able to quickly produce a new generic drug and put it into low-cost production at the Danyang City factory.

Eager not to jeopardise a sale of a drug that, due to legislation, may soon become more difficult to sell, Chang refuses to acknowledge there'll be any problems fulfilling our order over its proposed 12-month lifespan. The only obstacles, he claims, may, bizarrely, derive from political issues surrounding the execution of a mentally ill British man - 53-year-old Akmal Shaikh - in Urumqi in December.

'Your prime minister, Gordon Brown, asked China not to execute him but they put him to death anyway,' he says. 'Since then, relations between Britain and China have been a little sensitive and this is why we have to take a little care with our shipments.'

Out by the airport, however, it is apparent Chang has prepared for the new legislation. In a laboratory the size of a small apartment, a team of young scientists in white coats and face masks works on formulas that are not covered by the ban, ironically in a pharmaceutical zone where neighbours include multinationals Novartis, GlaxoSmithKline and AstraZeneca.

Dipping his nose into a sample bag of white powder presented to him by one of his scientists, Chang says: 'I can't tell you the name of this but it is going to be a good alternative to MDPV. It is going to be very popular and your buyers will be very interested.'

Scooping out a pinch between his fingers, he says: 'We have been working on this for some time and it is almost perfect and ready to ship. The purity is 99.9 per cent. If you look at it, you can see it is snow white. That shows how pure it is.'

When we press him for the ingredients of the new drug, he refuses to say, claiming that competitors would copy his secret formula and eat into his profits. With a typical display of immodesty, he says: 'I've called them Eric 1 and Eric 2.'

Inside the laboratory, the scientists appear to be working on a dozen different chemical processes at once. On one side of the room, huge bell jars containing drugs are undergoing an elaborate and colourful filtration process.

When we point out the extraordinary variety of colours in one of the bell jars and compare it with an oil painting, Chang laughs.

'You must be artists,' he says. 'When you look at that jar, you see colours. When I look at it, I see only orders and money.'

Driving us from the laboratory back to his downtown office in the hope of sealing another order, Chang is impatient to move on to the next deal. He has another group of overseas buyers dropping in, he says.

'I have no time for holidays. I work all the time,' he says, adding that he regrets seeing so little of his three-year-old son. 'One of the reasons I had this Buick imported is because I have so many European customers coming to visit and I need a big car to take them around because they have big bodies compared to Chinese people.

'This afternoon I have Russian customers coming to see me to place a big order. They want to buy MDPV and they want to look at the new product I have told you about as well. Of course, I have vodka ready for them - and Russian music, too.'

Chang might join them in a toast but he does not drink or smoke. Like most successful people on the money-making side of the industry, he doesn't indulge in the designer drugs he sells, either. His only personal vice, it seems, is a much more innocuous and strictly legal indulgence - he keeps cans of Red Bull handy in his Buick and in his office.

'It keeps me awake and alert when I work very long hours,' he says. 'I have so much business on my hands these days that I need all of the energy I can get.'