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.
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