By STEVE DOUGHTY

Last updated at 08:37 29 February 2008

Single and cohabiting women are increasingly much more likely to commit suicide than married women, a Whitehall report showed yesterday.

It found that those who do not marry were killing themselves at three times the rate of wives.

This is a much higher rate than 25 years ago, when single women were twice as likely to commit suicide as those who were married.

The findings, in a study by the Government's Office for National Statistics, suggest that cohabitation has made a high proportion of young women more vulnerable to depression.

They undermine Labour's dogma that all family relationships are equally good.

The major difference in the lives of women since the early 1980s is the spread of unmarried cohabitation and the decline in marriage.

The ONS said that between the early 1980s and 2004 marriage rates halved, but the number of single women under 50 in live-in partnerships trebled.

In 2004, more than a quarter of single women were cohabiting.

The study said that marriage has been seen as a protection against suicide since the Victorian era, when it was considered that being part of a couple improved the social integration of individuals.

It added that since a lot more unmarried people are now cohabiting, "we might expect relative differences in suicide rates between married and unmarried people to have become less clear cut over the last 25 years. This has not occurred."

Last night, independent researcher Patricia Morgan, author of the "Marriage Lite" study of the growth of cohabitation, said of the ONS report: "This is not a surprise, except to the Government.

"Cohabitation is a route to conflict, disappointment and unhappiness. Women tend to think if they shack up with someone, that is commitment.

"Men tend to think that means they get sex and shopping, but they are still free to look elsewhere."

Records show that overall numbers of suicides have gone down since the 1980s. But they have fallen much less sharply among single women.

In 1983, 18 in 100,000 single women committed suicide, and nine in 100,000 married women.

By 2004, there were 15 suicides in 100,000 single women and five among married women.

Among men, the likelihood of suicide has remained the same - single males are around three times more likely to kill themselves than husbands.

The ONS report said that studies abroad had shown that the higher risk of suicide was a result of remaining unmarried and not of other factors.

Labour set out its view on cohabitation ten years ago, when a Green Paper on family policy said that all kinds of relationships were just as good.

Since then, ministers have stripped away tax breaks for marriage, abolishing the Married Couples Allowance and removing all reference to marriage from tax and benefit forms.