The proportion of babies with at least one parent born overseas rose from a fifth to a quarter between July 2001 and 2006, according to the Office for National Statistics office (ONS).

A spokesman said: "We have figures for the contribution of mothers and fathers born abroad, and that has risen slightly, from under 20% in 2001 to slightly over 25% now.

"That reflects the cumulative effect of immigration over the last 40 years."

The overall population rose by 349,000 (0.6%) to 60,587,000 between mid-2005 and mid-2006, the figures indicated. This was slightly smaller than the 393,000 increase the previous year.

The overall number of births in the year to mid-2006 was 734,000, up from 718,000 the previous year. This latest figure was 71,000 more than in 2001.

The ONS attributed the rise to an increase in births to both UK- and foreign-born mothers. The evidence suggested the trend would continue, the spokesman added.

The flow of migrants into the UK in the year to mid-2006 was 574,000, 25,000 lower than in the previous year.

But a record 385,000 people migrated from the UK last year - the highest number since current counting methods were introduced in 1991 and 49,000 more people than in the previous year.

The statistics also showed the proportion of older people in the UK continuing to rise.

Record numbers of people were aged over 85 after a 6% increase to 1,243,000. The number of people of retirement age also rose by 1% to 11,344,000.

The five local authorities in England and Wales that experienced the greatest increase in population between 2001 and 2006 were Westminster and Camden, in London, South Northamptonshire, Forest Heath and Rutland. They all saw their populations swell by at least 11% over the period.