Cohabitation is a less stable form of relationship today than it was 15 years ago and particularly for couples with children, says relationships charity The Jubilee Centre.

A fresh analysis of national data by the centre shows that cohabitations are rarely a long term lifestyle choice and the vast majority last only a short time before being converted into marriage or dissolving.

Less than a quarter of first cohabitations last five years and just one in nineteen of all cohabiting couples (5.3 per cent) has been together for ten years or more.

The proportion of couples still cohabiting by the time their first child is 16 has dropped more than five-fold since the early 1990s. In contrast, marriage has become a more stable family background for children, with married couples now more than ten times as likely to stay together until their child is 16. Seventy-five per cent do so, compared with just 7 per cent of cohabiting ones.

The average unmarried couple now lives together for three years and almost a half stop cohabiting before two years. Around three in five couples who stop cohabiting decide to get married, while less than two in five separate, making marriage still the preferred relationship choice for couples.

Yet the analysis also showed that cohabitation does not serve as a ‘trial marriage’ but instead increases the odds of divorce. Never-married couples who cohabit before getting married are 60 per cent more likely to divorce than those who have not first lived together.

"Once again all the evidence suggests that families headed by married, biological parents who have not previously lived together provide the best environment for both the individuals involved and their children. This has huge personal, social, economic and political consequences for us all," said Jubilee Centre Director Dr John Hayward, who headed up the research,

Fellow researcher Dr Guy Brandon added, "The cost of family breakdown to society, whether parents have cohabited or married, is enormous. Besides the emotional cost, which inevitably has an impact on mental health and economic productivity, the direct costs are presently estimated at £41.7 billion each year – the equivalent of £1,350 per taxpayer per year.

"Given the projected rise in cohabiting couples in England and Wales from 2.25 million to 3.7 million in the next twenty years, and the clear link between cohabitation and family breakdown, it is fair to expect these costs to rise significantly in coming years."