A higher proportion of children are being brought up in one-parent families in Britain than in any other major European country.
One in five live with a single mother of father – a far higher ratio than in France, Germany or Scandinavian countries.
And while the number of married families in the UK is among the lowest in Europe, stable cohabiting relationships are also less common here than in other countries.
The figures, produced by the EU’s statistical arm, come at a time of increased efforts to downplay the importance of marriage by politicians and campaigners who oppose tax breaks for married couples.
Deputy Prime Minister Nick Clegg has declared that ‘strong relationships between parents are important’ but the state should not use the tax system to favour a particular family set-up.
The figures from Luxembourg-based Eurostat suggest that strong relationships outside marriage are uncommon in Britain but that the decline of marriage has meant life with a single parent for millions of youngsters.
These children are more likely than others to suffer poor health, do badly a school, and go on to less successful adult lives.
According to the breakdown, 20.8 per cent of children in the UK were living in single parent families in 2008.
In just three countries were children more likely to live with one parent: Estonia and Latvia in Eastern Europe, and Ireland, where the number was 23.2 per cent. It is believed the surge in Ireland is a result of generous benefits to single parent families and high immigration.
The proportion of children in single-parent families in the UK is roughly 50 per cent higher than in France and 35 per cent higher than in Germany.
The breakdown also makes it possible to check the share of children of single-parent families against those who live with married or cohabiting parents.
Around two thirds in this country are living with married parents, the analysis shows.
Apart from the small Eastern states of Estonia and Latvia, only France and Sweden have a smaller percentage of children in married families. But in both, children are much more likely to have cohabiting parents in a stable relationship.
According to the analysis, just 12.8 per cent of children in Britain are with cohabiting parents, compared with 27.3 in Sweden and 21 per cent in France.
Critics of cohabitation maintain that most such relationships are short-lived and many end by leaving behind single-parent families.
Those who want the Government to support married couples said yesterday that the figures proved the impact of tax breaks and the benefit system.
Researcher and author Patricia Morgan said: ‘You can look at these figures and see immediately which countries help couples through tax and benefits.
‘In France, people get help if they draw up legal family contracts. In Germany, Holland and Italy, married people get tax relief and tax relief for children. Even in Sweden, where they do nothing for married couples, they do not help single parents, and they expect them to work.
‘By contrast, our system encourages transient shack-ups. Even cohabiting couples get no help at all.’
Jill Kirby, an author on family development, warned: ‘Unless our Government acts to implement pro-marriage policies, the gap with the rest of Europe will continue to widen.’
Despite David Cameron’s pledge to introduce tax breaks for married couples, several Whitehall organisations are supporting cohabitation.
The Office for National Statistics is downgrading its publication of figures on marriage to give equal prominence to cohabiting families. And the Law Commission, the Government’s law reform adviser, is calling for legislation to help cohabitees settle inheritances and take out insurance policies.