Lone parents are "less effective" at raising children than their married counterparts, a former adviser to Nick Clegg claimed as he called for men to contribute more to family life.
Richard Reeves, the deputy prime minister's former director of strategy, claimed that while fathers have "greatly increased" their contribution to childrearing and housework "women continue to get the sharp end of the stick".
He called for breadwinning and childrearing to be shared equally to help improve modern family life and warned it would take more legal equality of rights and greater childcare to help that happen.
A transformation would help single mothers currently struggling to raise their children and ease the problem lower and middle-income families have giving their youngsters enough attention in the face of demanding work, he said.
In a report, The Symmetrical Family, he wrote: "In itself, the rise in lone parenthood has consequences for the size of the benefit bill since they are, by definition, more likely to be reliant on welfare - and indeed on the housing market, given the increased number of homes required. So there are significant knock-on effects for policy.
"But the most important, and most uncomfortable, fact is that lone parents are, on average, less effective parents. That's a stark statement but it is also an unavoidable one for anybody who has glanced at the research literature."
Mr Reeves, who will deliver a speech on the issue at a 4Children event, said: "At every level of society, greater gender equality will underpin better family life. If, and it is a big if, men are up to it. We are half-way through a revolution in the interaction between gender roles and family life. We have to keep going, and see similar changes in men's lives to the ones we have seen for women. By 2043, if we are successful, the terms 'career man', 'working father' or 'stay-at-home Dad' will have lost their novelty.
"The quality of family life is a collective concern. Poorly-raised children are a problem for our collective future. Talent and money are poured down the drain. When a family fails, we all suffer, even if only indirectly."