One us three women is still single at the age of 35
One in three women in UK is unmarried at 35
Marriage began to experience a decline in the 1980s, but in the last decade its popularity has fallen more sharply.
The downward trend corresponds with an increase in women following careers, the rising cost of buying a home and the growing acceptance of couples simply living together.
Analysts believe the introduction of tax credits to the benefit system since 1999 has dissuaded many from marrying, as they favour single mothers.
Figures show a couple with children must earn ￡50,000 a year between them before they are better off than if they lived apart.
The figures, from the Office of National Statistics, showed that fewer than two-thirds of women who reached 35 in 2005 had married - 665 from every 1,000.
Among those born five years earlier, nearly three-quarters had been married by 35.
About nine out of ten women who were 35 in 1990 had been married at least once.
However, the trend away from marriage seems at odds with the wishes of both men and women.
Previously polls have found that about seven out of ten still aspire to marriage.
Robert Whelan of the Civitas civic value think-tank said: "This is an incredible collapse, not just because of the extent but because of the speed.
"If it goes on we will soon see a majority of women unmarried in their mid-thirties.
"What we are seeing is a huge and growing gap between what people want in their lives and what they are getting."