Pre-nuptial agreements would be legally binding and cohabiting couples refused the same rights as those who wed, under Tory plans for strengthening marriage.
The proposals would see family laws reformed to bolster the access of fathers and grandparents to children.
State backing would also be given to classes to prepare people for tying the knot.
The changes have been drawn up by former Tory leader Iain Duncan Smith, who has been acting as David Cameron's expert on social breakdown.
Although Mr Cameron is not obliged to adopt the recommendations, he regularly stresses his commitment to supporting marriage and has previously looked favourably on Mr Duncan Smith's advice.
Mr Duncan Smith said his proposals were "timely" following the death of Baby P and other scandals that highlighted the "chaotic nature" of family life in some areas.
"This review is working from an underlying assumption that marriage should be supported both in government and in the law and that, related to this, fatherlessness - or motherlessness - should be avoided," he said.
"Policy can and should be focused on stemming the tide of relationship breakdown. Marriage acts as a stabiliser and a signal. Married couples are far less likely to break up than couples who live together without getting married.
"Today, 25% of children in this country live in single-parent families and this trend is set to accelerate. These children are three times more likely to experience abuse."
The interim report, from Mr Duncan Smith's Centre for Social Justice think-tank, advocates using the law and other official mechanisms to discourage "informal" relationships.
