The percentage of married adults is expected to fall to 48 per cent by 2011 and still further, to 45 per cent, by 2021, according to the Government Actuary Department. At present, married people make up 55 per cent of the population in England and Wales.
Couples who co-habit are likely almost to double in number - from 1.56 million in 1996 to about 3 million in 2021. But despite the dramatic rise, there will still be fewer people living as couples - married or unmarried - in the first quarter of the 21st century.
The Government's figures are based on the assumption that trends such as the fall in the marital rate for under 30-year-olds, the rise in the proportion of single (never married) people who co-habit, and the small increase in the divorce rate, will continue at the same rate.
The proportion of men who have never married is expected to rise from 32 per cent in 1996 to 41 per cent in 2021. For women, the figure is expected to rise from 24 per cent to 33 per cent over the same period.
A spokesman for the Church of England insisted last night that the decline in marriage was not a foregone conclusion. "If there is a downward trend, the question is, how long will it go on? Life is often cyclical... The church will continue to teach that marriage is the best way to cement a relationship and bring up children."
Divorce is likely to fall among younger age groups, but rise among the over-45s. The overall number of divorces among adults will rise from 8.55 per cent of all adults in 1996 to 11 per cent in 2021. Projected improvements in mortality mean the proportion of people who are widowed is to fall. It is expected that the number of widowed females over 65 will drop from 49 per cent in 1996 to 35 per cent in 2021.