Some separating parents need help from specialist services, but many turn to a doctor, teacher or lawyer.

The report confirms that children whose parents separate are nearly twice as likely to suffer long-term disadvantages, such as underperformance at school, poverty and depression. Children who undergo multiple family break-ups are particularly at risk.

The scale of the problem of family breakdown in England and Wales is shown in another report, published on Monday by the Institute of Economic Affairs, in which John Haskey of the Office for National Statistics says one child in four will experience the divorce of parents before reaching 16 if present divorce rates continue.

The authors of the Rowntree report - a review of more than 200 British research studies - stress that problems affect only a minority of children whose parents separate. In most cases the short-term distress, shown through bed-wetting and bad behaviour, fades.

They say parents should tell their children what is happening, keep them out of disputes and enable them to keep contact with both parents, says the report. The quality rather than the quantity of time with the non-resident parent is important.

The report, by Bryan Rodgers, of the Australian National University in Canberra, Australia, and Jan Pryor, of the University of Auckland in New Zealand, also dispels myths about the effects of divorce.

There is no consistent evidence that boys are more affected by divorce than girls (they may just show distress in different ways).

Calling for policy-makers to recognise the growing diversity of family structures, Jan Pryor said this week: “Support for parents and children may be just as important at the time of re-partnering as it is following separation. What is needed is a focus on parenting rather than on marital status.”

Patricia Morgan, family policy expert at the Institute of Economic Affairs, said: “Marital breakdown, putative fathers and unwed births have occurred whatever sort of family is regarded as the norm in a society. The only difference is that today’s new family forms are yesterday’s immoralities.”

Rather than accepting the current trend away from marriage as inevitable, politicians should devise policies to reverse it, she said and added:

“Men’s disengagement from families is of immense and fundamental significance for public order and economic productivity. This is something which is only just beginning to be acknowledged, as we blithely head for a situation in which 54 per cent of men aged 30 to 34 will be on their own by 2016.”

Divorce and Separation: the Outcomes for Children, published by the Joseph Rowntree Foundation, costs pound;11.95 plus pound;1.50 p amp; p from York Publishing Services, 64 Hallfield Road, Layerthorpe, York YO31 7ZQ . The Fragmenting Family: Does it Matter? costs pound;8 (including p amp; p) from IEA, 2 Lord North Street, London SW1 P 3LB.