They say this helped China achieve its stunning 10 per cent average growth rate over the past three decades, as well as easing the pressure on the country's highly polluted environment.
However, independent demographers question that 400 million population reduction claim, pointing out that the Chinese birth rate was already falling in the late 1970s before the one-child restriction came into force.
They also argue that the Chinese, in line with trends seen in other fast-developing countries, would have opted to have smaller families anyway as their incomes rose.
Nevertheless, the consensus is that the policy probably reduced the Chinese population by at least 100 million.
Human rights groups say the policy has led to brutal forced abortions and sterilisations, particularly in rural China.
It is also suspected of driving the growing gender imbalance in China, whereby there are six baby boys born for every baby girl today. A traditional preference for sons and the development of ultrasound scanning technology is thought to have interacted with the one-child policy to create an epidemic of selective abortions.
There are projected to be some 30 million young men in China by the end of the decade who will have no realistic hope of finding a Chinese spouse.
The one-child policy was never comprehensive, even in the earliest years. It did not cover China's 56 ethnic minority groups and families in the countryside were allowed to have an extra child if their first-born was a girl.
More recently, a growing number of wealthy families have opted to defy the two-child ban and to pay the heavy fines imposed. This is reported to have raised around $2.7b for the state coffers in 2012 alone.
The Communist Party also revealed yesterday that it intends to abolish its network of re-education through labour camps and increase the role of the free market in allocating resources in the economy as part of Xi Jinping's efforts to lay the basis for China's prosperity over the next decade.
- Independent