More than one in five births last year was to a mother born outside Britain, according to official figures published yesterday.

And almost 70 per cent of population growth over the next 25 years will be driven by the effects of direct and indirect migration, including births to immigrants.

Karen Dunnell, the national statistican, said: “We are seeing a quite dynamic change in the size of the overall population.”

Figures published by the Office for National Statistics show that between 2001-05 the population of non-white ethnic groups increased by 945,000, accounting for almost 11 per cent of the English population in mid-2005.

The mothers born in Bangladesh and Pakistan, the two biggest groups of mothers born outside Britain, accounted for 5 per cent of all births in the country last year.

Higher fertility rates among women born on the Indian subcontinent are highlighted in the office’s paper on the changing demographic picture of the UK.

Last year there were 154,000 births to non-British-born women, accounting for almost 21 per cent of total births in the UK.

The paper said: “Some groups have much higher fertility on average than UK-born women, in particular those born in Pakistan and Bangladesh.

“Other groups have fertility rates far more similar to those born in the UK, including women born in other EU countries, old Commonwealth countries, China and Hong Kong.”

Overall, however, the fertility rates in Britain are at the highest levels since 1980 among both British born and immigrant women. But it is still below that needed to keep the population at its current level without immigration.

The total fertility rate in Britain has risen from 1.5 children per woman to 1.7 between 2002 and 2006 but is higher among women born outside the country – a rise from 2.3 to 2.5.

Ms Dunnell said that women born outside the UK have slightly higher intended family sizes at each age range than UK-born women.

“Women born outside the UK are more likely than UK-born women to be intending to have large families. For example, 18 per cent of women born overseas aged 30-34 stated that they intended to have four or more children, compared to just 11 per cent of UK-born women of the same age.

“Analysis of actual family size indicates that women born overseas are indeed more likely to have larger families than UK-born women.”

However, Ms Dunnell’s analysis said that the higher average fertility rate of women born overseas may not continue with the second generation.

The study said the preliminary analysis comparing fertility rates of women born in Pakistan with women of Pakistan ethnic origin suggested that the fertility of second and subsequent generation migrants is lower than first generation and moves towards levels of UK-born women.

David Davis, the Shadow Home Secretary, said: “This shows all too clearly the impact immigration can have on the public sector infrastructure, including schools and hospitals.”

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