China, he said, is facing a crisis in development, growth and spiritual values which "will cause very serious social problems by the end of 1999 to the year 2003". He rejected government statistics which claim that China enjoys eight per cent economic growth. "Our conclusion is that the growth rate of the economy is actually zero, or even negative," he said. China's strategy of trying to catch up and overtake Western countries was damaging, and the policy needed to change: "China cannot be a superpower. It can only be a regional power."
Such sentiments are not the normal fare of public discourse in China - let alone of press conferences. But Mr Peng, 41, who last year set up a new research institute, believes that he can get away with expressing such views. "China's political leaders have a more open mind and the political environment has become more relaxed. Before the Clinton visit, China will not be so strict in this kind of thing."
President Clinton arrives in China on Thursday, and his visit will turn the world spotlight on the country's human rights record and the continuing restrictions on civil liberties and free speech. A letter signed by 71 dissidents yesterday urged him to remember the blood spilled in the Tiananmen Square killings nine years ago. The letter urged him to meet Bao Tong, the senior party member jailed in the crackdown, and others. The dissidents said that Mr Clinton would be stepping on "fresh, scarlet blood" in Tiananmen Square. The authorities remain jittery: in Xian, where Mr Clinton begins his trip, police yesterday held a Hong Kong reporter who is close to the dissident movement.
But the trip will also highlight a gradual change that may prove crucial, in the longer term - the cautious emergence in recent months of low-key political debate, and the growing number of quasi-independent grassroots civil organisations which have sprouted over the past five years.
Mr Peng - who has been everything from biology researcher and magazine editor to government official and real estate developer - recently registered in Hong Kong an environmental group, the China Development Union, which he claims is China's first genuine non-governmental organisation.
"We are not engaged in any secret activities. We seek co-operation with the Chinese Communist Party, we do not seek confrontation. We consider ourselves as a 'Third Force' in China," he said last week.
China's tolerance for any such "Third Force" remains very limited, as Mr Peng well knows. He approached more than 20 mainland publishers with the manuscript of The Fourth Landmark but none dared to publish it; he ended up going to a Hong Kong company. Nor, unsurprisingly, did any Chinese newspapers report on his press conference. Mr Peng stresses that the CDU is an environmental organisation, and not an ideological group. "We don't intend to become a political party."
Despite Mr Peng's protestations of innocence, the change in direction is clear. China operates a strict registration system for all organisations, which are forced to shelter under the administrative umbrella of some government unit. It was an irony of Peking's hosting of the NGO Forum at the UN Women's Conference in 1995 that, strictly speaking, China did not have any NGOs.
A number of organisations responding to new social problems have begun operating in a regulatory twilight zone. A Peking women's telephone hotline helps women cope with everything from the rising divorce rate, to ignorance about sex, to relationship problems, to coping with redundancy.
One woman, Xie Lihua, started a magazine called Rural Women Knowing All, distributed across the country, which aims to educate young, rural women in everything from health to marriage law, and how to cope with the difficulties of migrating to the cities to seek work.
At Peking University, faculty members and students run a free legal centre for women, offering advice to battered wives, female victims of sexual abuse and women fighting for their financial rights in divorce cases.
Such projects can justifiably claim to be in line with the government's policy of improving the lot of women - but they often stray into sensitive territory, implicitly questioning the authority of the state.
The first clear signs of change came after a Communist Party congress last autumn which enshrined the new leadership. Since then, a few academics and former officials have quietly broadened the political debate. Dissidents are still swiftly detained and sent for "re-education" for calling for democracy. Meanwhile, however, elderly figures from within the system are articulating the case for political reform.
In November, Fang Jue, 44, a former planning official in Fuzhou province, co-authored a declaration calling for a "new transformation". It said: "Taking the first step towards democracy is the key to China becoming a modern nation."
Since then, there has been a spate of articles and small meetings to debate political change. In January, the 76-year-old former vice-president of the Chinese Academy of Social Sciences published a magazine article which argued: "We should also champion political reform." Various political books, including an anti-Leftist blast by a former People's Daily editor, have become bestsellers in recent months.
There remain strict limits beyond which no one is allowed to venture. Most people who push at the boundaries are protected by high-level connections. Mr Peng said many former government officials had played a part in writing his book.
So far he has had no trouble since the news conference. What about after Mr Clinton has gone? "There could be some trouble," he says, "but I am not afraid."
Airport row, page 17; Boost for China, Business page 1