The rate of out-of-wedlock births in Britain is at its highest point for at least 200 years, according to a major new study of the history of the family from a leading think-tank.

Cohabitation levels have also soared from under five per cent pre-1945 to 90 per cent today, according to report by the Centre for Social Justice (CSJ) published on Monday.

The report, History and Family: Setting the Records Straight, shows that births outside marriage were at low levels throughout the 19th Century and stayed flat until the 1960s.

However since then the numbers have soared, from a five per cent that had remained constant over many decades to 45 per cent today.

Children brought up by lone parents on average do much less well than those brought up by two parents, according to a range of social science data.

For instance, they are 75 per cent more likely to fail at school and 50 per cent more likely to have alcohol problems. Separate studies have also shown that cohabiting couples with children are far less stable than married couples with children.

The latest report refutes claims made in a paper published last year by the British Academy that there is nothing new about contemporary levels of family breakdown.

The report, Happy Families? History and Family Policy, by historian Professor Pat Thane of the University of London was widely reported in the media. It claimed that there were high rates of ‘illegitimacy’ and cohabitation in the first half of the twentieth century.

However, figures stretching back to the 18th Century and examined by the latest report’s authors, Professor Rebecca Probert of Warwick University and Dr Samantha Callan, senior family researcher with the CSJ, shows that the 1960s marked a decisive break with 200 years of conventional family structure.

According to the historical figures they looked at, the percentage of births outside marriage in the England and Wales hovered around 5 per cent (except during the two world wars) until it began to rise in the 1960s.

The figures showed that, in the wake of the sexual revolution of that decade, the rate of births outside marriage rose steadily. By the late 1970s, this figure was above 10 per cent, by 1991 it was 30 per cent and today it is 45 per cent.

The figures examined by the report’s authors also reveal that the percentage of births outside marriage were the same in the 1950s as the 1750s at around five per cent.

The report also rejects suggestions that cohabitation levels, as opposed to marriage, were “high” in the early part of the 20th Century.

The authors point to research suggesting that in the 1950s and 1960s, showing that only 1-3 per cent of couples cohabited before marriage. Other research puts the pre-1945 level of cohabitation at four per cent. Today, nearly 90 per cent of couples live together before getting married.

The report also points to official records of unemployment claims from the 1920s which point to minimal levels of cohabitation.

The report acknowledges that not all marriages in the past “were happy and longlasting” and that there were “examples of successful and stable cohabiting relationships”.

But it adds:  “The fact that a number of marriages were brutal and fleeting should not obscure the centrality of marriage to family life in previous decades.

“While many Victorian marriages were short-lived because of the untimely death of one of the spouses, this does not mean that the experiences of the survivors were in any way comparable to those undergoing a divorce today.

“Similarly, while one can of course find examples from all historical periods of couples who lived together outside marriage, it does not follow that cohabitation was remotely as common in the past as it is today.”