FLYING postmen, falling leaves and fizzing fireworks brought a colourful climax to 40 days of Olympic and Paralympic triumph in Beijing last week. But no sooner had Boris Johnson exited the Bird's Nest stadium than the ruling Communist Party was rocked by an explosive scandal with far-reaching implications for post-Olympic China.

"On one side the Olympics, dancing and singing! On the other side, infants poisoned by no-quality food products! Is this the One World, One Dream' goal?" wrote an anonymous Chinese blogger on net portal NetEase.

"The victims are innocent children. Who will take responsibility for their losses? Who will make up for their future? Who will save the integrity of food safety?"

Traces of deadly melamine that had seemed confined to the baby formula of one Chinese dairy, Sanlu, have now turned up in batches from a further 21 companies, including the biggest, Mengniu, and Olympic sponsor Yili.

Government officials rushed to reassure reporters that there was no contamination of Olympic events even as more melamine was being uncovered by inspectors of mainland Chinese yoghurts and liquid milk in Hong Kong. The banned chemical used in plastics is added to diluted milk to make it appear higher in protein.

With four infants dead so far and 6244 sickened with kidney stones, China's State Council issued a statement that "most" of China's baby formula was safe. That did not include China's top three dairy brands, according to the nation's quality control watchdog agency.

The official Chinese media launched with gusto into a new campaign of milk inspections, milk crackdowns, milk sackings and milk arrests, including ever-more diabolical claims about the Geng brothers, milk merchants accused of adding melamine to baby formula.

Li Changjiang, the nervous head of the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ), boldly asserted that milk production would be safe for expansion "in a short period of time".

Few Chinese consumers were buying. Chatting online and crammed in hospital waiting rooms across China, they recalled similar pledges from the 2004 bogus baby formula scandal that killed at least 12 youngsters.

Others mentioned the in-depth investigative Chinese TV programme Weekly Quality Report, broadcast on September 2. A reporter spent 10 days investigating Sanlu's advertising claim that its milk underwent 1100 tests and found it wholly accurate.

Satirists, meanwhile, savoured the memory of the late Zheng Xiaoyu, former director of the State Food and Drug Administration, who in 2005 vowed to root out official corruption. He was executed by firing squad on July 10 last year for taking bribes.

"I do think they should all be executed," Michelle Guo, Beijing mother of one-year-old Ricky Zhao, told the Sunday Herald. "And I don't mean they round up the usual suspects, a local leader and a few innocent farmers. I mean every single one of them, all of those who knew the truth, at all levels. I don't care how many."

China's Great Firewall prevented Guo from knowing that it was in fact New Zealand's prime minister, Helen Clark - and not a domestic leader - who had blown the whistle. Clark's government complained to Beijing, she said, after local officials had "put a towel over" the scandal. New Zealand dairy giant Fonterra, 43% owner of the Sanlu group, which is based in Shijiazhuang, Hebei Province, had also been "trying for weeks" to persuade officials in China to announce a recall, she said.

The delay was caused by the Olympics, many China analysts believe. They point to edict No.8 in the secret "21-Point Directive On Reporting Olympics" promulgated by China's top propaganda organ: "All food safety issues, such as cancer-causing mineral water, is off-limits."

Hebei vice-governor Yang Chongyong confirmed that Shijiazhuang city officials delayed reporting the poisonings during August when Beijing was hosting the Olympics. Sanlu, he added, had "already covered up many of the facts" before reporting the problem on August 2.

The first reported death, of a five-month-old boy, occurred three months earlier on May 1. Chinese citizen journalists have also unearthed a May 12 bulletin board posting by 40-year-old Wang Yuanping alleging that he received four cases of milk for silence about his daughter's sickness. Wang said he regrets taking the bribe, but "trying to reveal the truth about an incident is sometimes very hard."

Until a week ago, Sanlu's baby milk formula came with a seal stating "no inspection needed": their 1100 tests met the highest possible standards of government approval. That's a little sticker with big implications, according to Tao Jingzhou, legal expert at Jones Day law firm in Beijing.

"All these companies have a connection with the authorities. Their products were not subject to inspection," he said. "So the question should really be whether the victims can sue the Chinese government."

In an unprecedented stand yesterday that will test the Communist Party's limits on civil society, more than 70 human rights lawyers from 23 provinces and municipalities announced they will help parents whose babies are sick or have developed kidney stones from drinking tainted infant formula.