In what is the Coalition's clearest pro-marriage intervention since it was formed, Iain Duncan Smith will say that it is "absurd and damaging" for ministers not to extol the benefits of marriage for fear of stigmatising those who choose not to marry.
The Work and Pensions Secretary will argue that the current system of benefits is "crazy" because it stifles people's genuine aspirations to build and commit to a strong family. He believes marriage has become the preserve of the better off.
Mr Duncan Smith will say: "We do a disservice to society if we ignore the evidence which shows that stable families tend to be associated with better outcomes for children."
He will add: "There are few more powerful tools for promoting stability than the institution of marriage."