One in five babies born in Britain last year was born to a woman from overseas, according to the first official analysis of the impact of migration on fertility.
Immigrant mothers are having far more children than their British counterparts—fuelling the biggest rise in population since the 1960s baby boom.
The highest birth rates were among Pakistani, Indian or Bangladeshi-born mothers, who gave birth to five per cent of all UK babies last year.
A further four per cent were born to mothers from EU countries outside Britain and Ireland, with a growing number from eastern Europe.
The Pakistani rate of 4.7 children per mother is almost three times higher than the British rate of 1.7.
The study, by the Office for National Statistics, shows that about 150,000 of the 749,000 births—21 per cent—were to immigrants. This compares to 15 per cent in 2001.
Almost 70 per cent of the 10 million rise in population over the next 20 years will be attributable to immigration—either directly or via higher birth rates—if trends continue.
Over the past five years alone, immigration has added more than one million to the population. One estimate recently suggested that a combination of higher birth rates, an ageing population and record immigration could push the population above 100 million in 50 years.
Fertility rates have in the past been the key to ensuring a rising population, which has historically been the engine of economic growth.
But families need to have at least two children to replace the population assuming zero immigration.
This so-called “replacement rate” was easily achieved throughout most of British history until the 1960s.
But declines in subsequent years reduced the fertility rate to just 1.6 by 2001. Since then, however, immigration has helped to push it up again.
Karen Dunnell, the National Statistician, said that while an average of 1.7 children are born to UK mothers, among migrant mothers the number is 2.5.
While fertility is highest among immigrant mothers, it is also rising for the first time in many years among British mothers as well.
Many women are having children later in life but there has also been an “unexpected” increase in fertility among younger females aged 20 to 24.
The study says: “Since 2001, fertility rates have stopped falling and in the 25-29 age group have started to increase. Possible explanations for this change may be changes in maternity leave, taxation and benefits for those with children and also the impact of recent levels of international migration to the UK.”