The numbers are startling. Only 3.2 per cent of Spain's population was foreign-born in 1998. In 2007 it was 13.4 per cent. Europe's Muslim population has more than doubled in the past 30 years and will have doubled again by 2015. In Brussels, the top seven baby boys' names recently were Mohamed, Adam, Rayan, Ayoub, Mehdi, Amine and Hamza.
Jerome Vignon, the director for employment and social affairs at the European Commission, said that the focus of those running the EU had been on asylum seekers and the control of migration rather than the integration of those already in the bloc. "It has certainly been underestimated - there is a general rhetoric that social integration of migrants should be given as much importance as monitoring the inflow of migrants." But, he said, the rhetoric had rarely led to policy.
The countries of the EU have long histories of welcoming migrants, but in recent years two significant trends have emerged. Migrants have come increasingly from outside developed economies, and they have come in accelerating numbers.
The growing Muslim population is of particular interest. This is not because Muslims are the only immigrants coming into the EU in large numbers; there are plenty of entrants from all points of the compass. But Muslims represent a particular set of issues beyond the fact that atrocities have been committed in the West in the name of Islam.
America's Pew Forum on Religion & Public Life, part of the non-partisan Pew Research Center, said in a report: "These [EU] countries possess deep historical, cultural, religious and linguistic traditions. Injecting hundreds of thousands, and in some cases millions, of people who look, speak and act differently into these settings often makes for a difficult social fit."
How dramatic are the population changes? Everyone is aware that certain neighbourhoods of certain cities in Europe are becoming more Muslim, and that the change is gathering pace. But raw details are hard to come by as the data is sensitive: many countries in the EU do not collect population statistics by religion.
EU numbers on general immigration tell a story on their own. In the latter years of the 20th century, the 27 countries of the EU attracted half a million more people a year than left. "Since 2002, however," the latest EU report says, "net migration into the EU has roughly tripled to between 1.6 million and two million people per year."
The increased pace has made a nonsense of previous forecasts. In 2004 the EU thought its population would decline by 16 million by 2050. Now it thinks it will increase by 10 million by 2060. Britain is expected to become the most populous EU country by 2060, with 77 million inhabitants. Right now it has 20 million fewer people than Germany. Italy's population was expected to fall precipitously; now it is predicted to stay flat.
The study for the US Air Force by Leon Perkowski in 2006 found that there were at least 15 million Muslims in the EU, and possibly as many as 23 million. They are not uniformly distributed, of course. According to the US's Migration Policy Institute, residents of Muslim faith will account for more than 20 per cent of the EU population by 2050 but already do so in a number of cities. Whites will be in a minority in Birmingham by 2026, says Christopher Caldwell, an American journalist, and even sooner in Leicester. Another forecast holds that Muslims could outnumber non-Muslims in France and perhaps in all of western Europe by mid-century. Austria was 90 per cent Catholic in the 20th century but Islam could be the majority religion among Austrians aged under 15 by 2050, says Mr Caldwell.
Projected growth rates are a disputed area. Birth rates can be difficult to predict and migrant numbers can ebb and flow. But Karoly Lorant, a Hungarian economist who wrote a paper for the European Parliament, calculates that Muslims already make up 25 per cent of the population in Marseilles and Rotterdam, 20 per cent in Malmo, 15 per cent in Brussels and Birmingham and 10 per cent in London, Paris and Copenhagen.
Recent polls have tended to show that the feared radicalisation of Europe's Muslims has not occurred. That gives hope that the newcomers will integrate successfully. Nonetheless, second and third generations of Muslims show signs of being harder to integrate than their parents. Policy Exchange, a British study group, found that more than 70 per cent of Muslims over 55 felt that they had as much in common with non-Muslims as Muslims. But this fell to 62 per cent of 16-24 year-olds.
The population changes are stirring unease on the ground. Europeans often tell pollsters that they have had enough immigration, but politicians largely avoid debate.
France banned the wearing of the hijab veil in schools and stopped the wearing of large crosses and the yarmulke too, so making it harder to argue that the law was aimed solely at Muslims. Britain has strengthened its laws on religious hatred. But these are generally isolated pieces of legislation.
Into the void has stepped a resurgent group of extreme-Right political parties, among them the British National Party, which gained two seats at recent elections to the European Parliament. Geert Wilders, the Dutch politician who speaks against Islam and was banned this year from entering Britain, has led opinion polls in Holland.
The Pew Forum identified the mainstream silence in 2005: "The fact that [extreme parties] have risen to prominence at all speaks poorly about the state and quality of the immigration debate. [Scholars] have argued that European elites have yet to fully grapple with the broader issues of race and identity surrounding Muslims and other groups for fear of being seen as politically incorrect."
The starting point should be greater discussion of integration. Does it matter at all? Yes, claims Mr Vignon at the European Commission. Without it, polarisation and ghettoes can result. "It's bad because it creates antagonism. It antagonises poor people against other poor people: people with low educational attainment feel threatened," he says.
The EU says employment rates for non-EU nationals are lower than for nationals, which holds back economic advancement and integration. One important reason for this is a lack of language skills. The Migration Policy Institute says that, in 2007, 28 per cent of children born in England and Wales had at least one foreign-born parent. That rose to 54 per cent in London. Overall in 2008, 14.4 per cent of children in primary schools had a language other than English as their first language.
Muslims, who are a hugely diverse group, have so far shown little inclination to organise politically on lines of race or religion. But that does not mean their voices are being ignored. Germany started to reform its voting laws 10 years ago, granting certain franchise rights to the large Turkish population. It would be odd if that did not alter the country's stance on Turkey's application to join the EU. Mr Perkowski's study says: "Faced with rapidly growing, disenfranchised and increasingly politically empowered Muslim populations within the borders of some of its oldest and strongest allies, the US could be faced with ever stronger challenges to its Middle East foreign policies."
Demography will force politicians to confront these issues sooner rather than later. Recently, some have started to nudge the debate along. Angel Gurría, the OECD secretary-general, said in June: "Migration is not a tap that can be turned on and off at will. We need fair and effective migration and integration policies; policies that work and adjust to both good economic times and bad ones."