Nearly two-thirds of children adopted in Britain last year were aged between one and four, official figures show.

The 2011 figure was up on the previous year, when one- to four-year-olds made up 58 per cent of adoptions in England and Wales, the Office for National Statistics said.

There was also a six per cent rise in the overall number of adoptions, with 4,734 in 2011 compared with 4,481 in 2010. Meanwhile, the percentage of children adopted who were born outside marriage increased to 82 per cent last year, up from 80 per cent in 2010.

The percentage of adopted children aged one to four has steadily increased since 1998, when the proportion was only 34 per cent.

At the same time, adoption in other age groups has decreased. The percentage of under-ones was five per cent in 1998 compared with two per cent in 2011. For children aged between five and nine, the proportion has decreased from 36 per cent in 1998 to 23 per cent last year.

The percentage of children between 10 and 14 being adopted has more than halved from 21 per cent in 1998 to one in 10 in 2011. The percentage of adopted children aged 15 to 17 has decreased to two per cent, from five per cent in 1998.