There were 17.1 million families in the UK in 2006 - up from 16.5 million in 1996.
Most were still headed by a married couple (71%), although the proportion of cohabiting couple families had increased to 14%, from 9% 10 years earlier.
Although two children remains the most common family size, the average number of children per family in the UK has dropped - from 2.0 in 1971 to 1.8.
WHERE FAMILIES LIVE
More young people are living at home for longer. In 2006, 58% of men and 39% of women aged 20-24 in England still lived at home with their parents.
There is a larger than average concentration of single people living in London, whereas married couples and families tend to be concentrated in the centre of the country and around the outskirts of major cities, according to research by Professor Danny Dorling of Sheffield University.
His map is based on data drawn from the 85 constituencies used for the European parliamentary elections in 1999, each containing roughly half a million people over the age of 18 in a similar geographical area.
The areas are categorised, for example as predominantly single, where the number of people living on their own is the most unusually large group compared with the national average.
Figures were not available for Northern Ireland.
In most families with dependent children, the father is still the main wage earner and the mother often works part-time.
According to the BBC/ICM poll, 33% of women still do the bulk of household chores, but 35% of respondents said both parents shared childcare duties.
The average family income is £32,779 before tax.
According to ONS figures, an average household - made up of 3.9 people - spends £601.20 a week, compared with a couple's average spend of £527.30. In other words, the household spends £155.60 per head, compared with a couple's spend of £263.60 per head.