The Family: Average age for first-time mothers higher than ever: The Government's statistical survey depicts prosperous and well-educated Britons deserting 'traditional' lifestyles. David Nicholson-Lord reports

THE AGE at which women are having their first baby is higher than ever. The proportion of births outside marriage has more than doubled in the past decade. And for every two marriages in 1991 there was one divorce.

The theme of families under stress, central to recent political debates on single parenthood and the Government's back to basics campaign, is confirmed in the latest issue of Social Trends, the Central Statistical Office publication which aims to provide a 'biography' of British society.

The 24th edition, published today, coincides with the International Year of the Family. It depicts a Britain wealthier, healthier and probably better educated than ever but with the 'traditional' family subjected to increasing strains through cohabitation, marriage break-up, lone motherhood and new work patterns.

Among the statistical highlights is the age at which women have their first child within marriage. At 27.8 years in 1992, this is the highest on record, part of a trend towards older child-bearing evident since the early 1970s. In the 1980s, fertility rates for women in their twenties fell. For teenagers, it rose by 18 per cent. For women between 35 and 39 it rose by 48 per cent.

Some of the changes to marriage, while of long-standing, have accelerated in the past decade. The proportion of births outside marriage, for example, has been increasing since the late 1950s but took more than 20 years to rise from 5 to 10 per cent of all births.

By 1992, one in three births was outside marriage: more than half of these, however, were registered to parents at the same address, indicating a stable relationship. Nearly one in five unmarried men and women aged between 16 and 59 were cohabiting in 1992.

But Social Trends also throws light on the rise of lone parenthood. Out of 7.2 million mothers in 1991, nearly 1.2 million were single parents. As a proportion of all families with children, one-parent families nearly doubled between 1976 and 1991, from 10 to 19 per cent.

Family patterns also vary with ethnic background. In 1961 more than half of people in Britain lived in a household made up of a couple with dependent children. In 1992 the figure had fallen to 40 per cent.

However, the 'traditional' family structure is still relatively common among households of Asian origin - Bangladeshis, Pakistanis, Indians and Chinese. It is least common among blacks. And more than half of West Indian mothers were single parents - compared with one in ten Pakistani and Bangladeshi mothers and one in six whites.

Solitary living continues to increase. Twenty-seven per cent of households in 1991 consisted of one person living alone - up from 22 per cent in 1981 and 14 per cent in 1961. Female pensioners formed the largest group of one-person households but the biggest rise has come in men under pensionable age. Nearly one in ten households in Britain at the end of the century will consist of a man under 65 living alone.

Social Trends; HMSO; pounds 27.

(Graphs omitted)