Births have replaced immigrants in the UK as the main reason for the country's population expansion, official data shows.

In the past year, the overall population has grown by 408,000 - the biggest annual growth - to reach 61.4 million. But it is not because of an influx of migrants. A total of 791,000 babies were born in 2008, according to Office of National Statistics data released this week, and 56 percent of those babies were born to non-British mothers.

Economic recession has led couples to spend evenings at home and may have led to a rise in pregnancies, according to ONS chief statistician Karen Dunnell.

Migrant workers, while rising by 561,000 in 2008, compared with 605,000 in 2007, were slowing in numbers coming to the UK.