Similar restrictions on the other perks of multiple parenthood can only be a matter of time.The truth is that France missed the demographic bus 200 years ago. It broke with more than a century of procreation policy in France by imposing a means test on family allowances. The definition of a famille nombreuse was reduced to three children, and the benefits increased, as recently as 1982.Mr Quang has studied the effects of family subsidies on French fertility rates and population growth: his conclusion, backed by other studies, is that they have no discernible impact. The French fertility rate - now 1.72 children for every woman of child-bearing age - is marginally above the European average, but little different from the rate in Britain.Last month the new Socialist-led government in France did something brave and sensible, without quite admitting it. In other words, if France had grown as fast as Britain it would have a population of 150,000,000 today.By the middle of the 19th century, the French were worried by their shortage of children; there was a "preoccupation du desert", an obsession with emptiness, according to another French demographic expert, Quang-che Dinh. This was reinforced by the slaughter in the trenches in the First World War; but, in fact, those losses were more than made up by Spanish and Italian immigration in the 1920s and 1930s.The defeat in 1940 - when Germany mobilised 40 divisions to France's 10 - led to something like "demographic panic", according to Mr Quang.The Vichy government enormously increased subsidies to families, partly for ideological reasons But the policy was pursued vigorously post-war.

France, which had for centuries been the most populous, and one of the most thickly populated, European countries, saw other nations catch up and even go ahead. At the beginning of the 19th century, there were 27,600,000 people in France and about 10,500,000 in Britain Both countries now have about 58,000,000. Families, even poor families, wanted to cherish a small number of children rather than neglect them in large numbers.For whatever reason, the French birth-rate collapsed long before it did elsewhere. Advances in medicine and diet stopped people dying young but, for several decades, the birth rate remained as high as ever: as a consequence, the European population leaped.But not in France.

Why they did this remains a mystery: some historians put forward economic explanations; others suggest that it was something to do with Jean-Jacques Rousseau and the cult of the child. French people also stopped dying young (if they avoided the guillotine) but they also stopped having so many children. Long before other countries, the French began to practise birth control, mostly though coitus interruptus, according to Mr Touleman, since condoms were not yet widely available. Every other European country had a population explosion in the late 18th and early 19th centuries. But Laurent Touleman, a demographic expert at the French statistic institute, explained that the phenomenon is, in fact, much older. It will also give us free admission to museums, swimming pools and play-grounds.I am, of course happy to claim the benefits, grace a baby Grace, but they also made me curious.Does any of this largesse do any good? Does it really encourage French people to have babies? Why is France so empty in the first place?The low population density, by European standards, is sometimes attributed to the slaughter of young French males during the First World War. Once I have lived in Paris a little longer, I will qualify for a Paris-Famille card: this will give me pounds 200 a year towards metro travel, car tax, school meals or child care.