David Cameron has reignited the family values debate by claiming marriage could fix the UK's "broken society".
Speaking ahead of the Tory's social justice policy review into social breakdown, Mr Cameron called for a reform of the tax and benefits system to encourage marriage.
The Tory leader insisted he was not forcing marriage as the only correct model, but insisted it was a good institution which should be supported by the state.
He called on politicians to scrutinise the tax and benefit system "and ask ourselves why it is encouraging people to live separately".
Mr Cameron said: "The point I am making is that marriage is a good institution. It should be supported. It should be recognised in the tax system."
Despite its growing economic health, there is something "deeply wrong" in society and family breakdown is at its heart, Mr Cameron said.
Justifying state intervention, he pointed to high levels of teenage pregnancy, educational under achievement, drug abuse and anti-social behaviour.
He repeated statistics suggesting parents who marry are more likely to stay together if they marry. Half of unmarried couples split before their child's fifth birthday, compared to one in 12 married couples.
Mr Cameron continued: "The evidence is incredibly strong. We need a big cultural change in favour of fatherhood, in favour of parenting, in favour of marriage.
"I think it is absolutely the big question, the big argument of our times. Kids do best if mum and dad are there to look after them. And today we have a benefits system that encourages families to break up, encourages couples to separate.
"We have no recognition of marriage in the tax system. These things have got to change."
The Conservatives' social justice policy review taskforce, headed by former leader Iain Duncan Smith, is due to make its recommendations tomorrow.
As well as tax breaks for married couples, it is expected to say young people who take part in volunteer work should be rewarded with treats such as gig tickets. It will also recommend an increase in the cost of alcohol and the reclassification of cannabis as a class B drug.
The Liberal Democrats dismissed the report, insisting the Conservatives were offering 19th century solutions to 21st century problems.
Lib Dem families spokesman David Laws said most of Britain's social problems could be traced to the Tories' 18 years in office.
"Child poverty soared, male unemployment rocketed, social mobility declined and family life fell apart," he said.
Mr Laws added the latest Conservative policies marked a step backwards and instead the UK needed "real reform" to boost social equality and integration.
The Labour government has resisted calls for a married couple's allowance, arguing state help should be targeted at the most disadvantaged families.