A SOCIAL revolution is under way with the emergence of a new form of committed relationship in which couples do everything together while maintaining separate housesholds.

An estimated one million couples now fall into this classification, known as Living Apart Together, or LAT, according to the first study of the phenomenon published yesterday by the Office for National Statistics. The study found that 3 in every 20 men and women aged 16 to 59 who are neither currently married nor cohabiting are LATs.

Many may be divorcees with children, who fear that moving the whole family in with a new partner may be too complicated. Some may be professionals who have jobs in different cities or countries. Others may have to move from a partner to care for a relative in another town. Older couples may decide to stay apart to ensure that their children and grandchildren inherit their property.

Then there are couples who, having already loved and lost, have become “risk averse”, according to John Haskey, of Oxford University, who wrote the study.

“It is not about a lack of commitment or an increase in individualisation. It’s very much that caution is holding people back from situations they saw as risky,” Mr Haskey said.

He added that the findings could have far-reaching implications for public policy, notably on housing. “There has been a substantial increase in living alone — almost one in three households contains only one person. It might previously have been thought that people living alone had no partner — but some undoubtedly do in a Living Apart Together relationship. Should LAT grow in the future, more accommodation for one person units will be required,” he said.

When the student population and teenagers living at home are taken into account, the number of LATs rises to two million men and two million women, but Mr Haskey has excluded these as many of them will simply be couples who are dating. “It is possible that couples may Live Apart Together before moving in together before marrying, in this case, LAT can be thought of as pre-pre-marital cohabitation,” he added.

LAT-ing is most common among the 30 to 34-year-old age group, where about 20 per cent of people fall into the category. Mr Haskey said it was impossible to say from his study, which is based on a sample of 5,500 adults from the 2002-03 General Household Survey, whether LAT-ing was on the increase, but other relationship experts say it is.

Suzie Hayman, of Parentline Plus, who is to present a new BBC One series on step-families, said that LAT-ing was a recognition that in step-families there are two things going on. “There is the relationship between the adults, which the adults see as a new beginning, and then there is the relationship between the adults and their children, which the children see as being threatened. One way of sorting this out is to keep the two relationships apart in separate households,” she said.

Fiona Williams, Professor of Social Policy at the University of Leeds, said that even when housing costs were high, people who could afford to were deciding to “tread carefully and respect each others’ space” before deciding whether to move in together. “It has often been assumed that the growth of so-called “singletons” in their late 20s and early 30s reflects a more atomised and lonely society. In fact, what these new statistics seem to indicate is the growth of a new type of relationship arrangement,” she said.

Ceridwen Roberts, of Oxford University, said it was also possible that single parents who formed new relationships may choose to live separately because the would lose state benefits, such as tax credits, if they married or cohabited. This was nothing to do with the tax credits, but had always been a feature of the benefits system, she added.

• Separate ONS data shows that for the first time women in their early 30s have higher fertility rates than women in their late 20s. Although fertility rates increased in all age groups the trend towards later childbearing continues. The fertility rate among women aged 30-34 was 99.4 live births per thousand women, an increase of 4.9 per cent on 2003, and the highest in any age group since 1998.

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