Couples under 45 without children are more likely to be cohabiting than married according to a new report from the Economic and Social Research Institute (ESRI)

The report also reveals that cohabiting couples are very likely to marry once their first child is born, confirming the link in the public mind between marriage and children.

In addition, 25pc of cohabiting couples contain at least one partner who is separated or divorced following a previous marriage.

The average age of the group of cohabiting couples containing at least one person from a previous marriage is over 40 and it includes couples in their 50s and 60s, illustrating that older people in Ireland also took advantage of the growing acceptability of cohabitation, the report adds.

In another sign of changing social mores, people with a Leaving Certificate education now have the most children. In the past, poorly educated people tended to have the most children.

Those with higher levels of education still have children later in life, however.

The chance of living with two married parents is much higher where parents have a high level of education.

The report also says: “Couples still mostly form among people with similar levels of education and similar occupations, but there has been a striking shift in the gender balance in this regard.

“Among couples with a mean age of 26-40, the woman has a higher level of educational attainment in 34pc of couples, versus 16pc where the man has. In 42pc of cases she has the higher occupational classification, as against 28pc where he has.

“This represents a radical change from previous generations: among couples with a mean age of 56 70, the gap in educational attainment is much narrower (26pc versus 21pc) and the man is more likely to have the higher occupation (31pc versus 36pc).”

At least 2.5pc of children live in step-families and at least 1.3pc are step-children.

Ireland still has a low overall level of second relationships and remarriage.

Younger couples are more likely to bridge social boundaries, including between religious beliefs, different nationalities and ethnicities, the report says.

This may reflect a more open approach or simply reflect more opportunity, the researchers add.