An investigation by Sky News uncovered a chain of supply from factories to British dealers.
The channel said it had discovered an entire new generation of chemical highs including substances such as methylone, butylone and MDPV. All of them mimic the effects of drugs such as cocaine and ecstasy.
Posing as a potential customer, Sky News correspondent Holly Williams contacted a Shanghai-based company and was told by that the company makes both mephedrone and methylone "in batches – 100 kilograms, 200 kilograms, 50 kilograms, whatever the customer wants".
The worker went on to reveal that the company already has five British customers.
She said: "One of them orders 50 to 100 kilograms a week. The other one orders 50 kilograms of mephedrone a month, and 40 kilograms of methylone."
Asked whether a British ban on mephedrone would cause problems, the worker said the company was already well prepared.
"We're working on five or six new legal products," she said. "Most of them come from our British customers. They told us how to make the new ones."
Toxicologist Dr John Ramsey told Sky: "We're seeing 10 or 11 new compounds every year coming out now. The Chinese chemical industry seems to provide anything at a price."
The Advisory Council on the Misuse of Drugs is considering a ban on mephedrone after it was linked to the deaths of a number of young people.
Ministers are expected to receive its report today and are set to rush through legislation to outlaw the substance which has been linked to three deaths in the region.
Gordon Brown said he was "ready to take action" after the death of Lois Waters, 24, from Malton, who was found dead at a friend's house after taking the drug during a weekend out with friends.