Living together is just as good as being married, even when it comes to bringing up children, British people now believe.

Fewer than a fifth of people think there is much difference between being married or living together and more than half (53 per cent) say that weddings are more about celebration than life-long commitment.

A comprehensive study of public opinion found that only 28 per cent think married couples make better parents than unmarried pairs and there is broad support for step-families, who are widely seen to be doing a good job. More than three quarters of the public believe that a mother and a stepfather could bring up a child just as well as two biological parents.

The research also discovered that most people think divorce is a normal part of life, with two thirds saying that it can be “a positive step towards a new life”. Even when children are involved divorce is no longer seen as a disaster, with 78 per cent of the public saying the end of a marriage in itself does not harm children, although conflict between parents does.

Only 30 per cent said that divorce should be made more difficult for parents with young children, with four in ten disagreeing.

The findings, in this year’s annual survey of British Social Attitudes, helps to explain why the rate of marriage has plummeted to a 100-year low. The number of Britons choosing to get married fell to the lowest level in 111 years in 2005, when only 244,000 weddings took place.

People are more divided when it comes to lone parents. Fewer than half (42 per cent) say that single parents are as good as two parents to bring up children, and only 44 per cent say that women who live alone should have a child if they want one.

The one remaining taboo appears to be extramarital affairs. An overwhelming majority (84 per cent) said that extramarital sex was always wrong, the same proportion as 20 years ago when records first began.

The report’s authors said that the last 20 years had brought a dramatic liberalisation of attitudes towards family life.

Alison Park, co-author of the report, said: “The key finding is that people’s views about marriage and cohabitation are clearly getting more liberal, although it only goes so far once children enter the equation.

“The public are divided about one parent bringing up children, although when it comes to step-parenting they feel you don’t need to be biological parent and you don’t need to be married to do a good job.”

Historical data suggests that attitudes towards marriage began to liberalise not in the 1960s and 1970s, often seen as the decades of huge change, but in the 1980s and 1990s. Only 2 per cent of women had lived with a partner by 1969 and only 11 per cent by 1979. That figure rose to 29 per cent in 1999.

Today’s report may serve as a warning to David Cameron, who intends that the Conservatives will offer tax breaks for married couples with children at the next election.

Family campaigners said they were disappointed that the public thought cohabiting and marriage were the same. Research showed that married parents did better at staying together.

Harry Benson, head of the Bristol Community Family Trust, said: “The findings are not surprising. It is socially acceptable to live together, the government says doesn’t matter if you are married or not. From the outside if looks the same whether you are married or not.

“But the outcomes show that it is not the same. Cohabiting parents are twice as likely to split up before their child is five than married couples and outcomes are the thing that matter,”

He agreed that conflict is more damaging for children than separation. “But that is all the more reason for unhappily married couples in a low-conflict relationship who have drifted apart to really make an effort to stay together. They can rebuild their marriage, and the evidence suggests when divorce comes out of the blue it is the most damaging for children.”

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