David Cameron has reaffirmed his commitment to the institution of marriage and the importance to children of stable relationships.

His words come a little over a week after a leading UK think tank said that he had broken his promise to support marriage and tackle marital breakdown.

However, Ed Miliband, the leader of the Opposition, has insisted that marriage does not automatically make families more stable.

In a keynote speech, Mr Cameron accused the last Labour government of focusing too much on ploughing money into children’s services, without appreciating that it is stable families who provide the prerequisite for a happy life in adult years.

By supporting relationships – preferably within the context of a marriage – the Government will in future put families at the heart of policy making.

The Prime Minister’s recommitment to the importance of marriage comes as he uses a major speech to attempt once again to define his crusade of the Big Society.

However, only 12 days ago, the Centre for Social Justice, an influential think founded by former Tory leader and Cabinet colleague Iain Duncan Smith said that since he became Prime Minister, Mr Cameron had done little to support marriage.

It also strongly criticised the Coalition plans to cut child benefit for middle-class parents.

Mr Cameron said: “Now I have always made it clear what I think about the family. I think families are immensely important.

“I am pro-commitment, I back marriage and I think it’s a wonderfully precious institution.

“Strong familes are where children learn to become responsible people. When you grow up in a strong family, you learn how to behave, you learn about give and take.

“You learn about responsibility and how to live in harmony with others. Strong families are the foundation of a bigger, stronger society. This isn’t some romanticised fiction. It’s a fact.

“There’s a whole body of evidence that shows how a bad relationship between parents means a child is more likely to live in poverty, fail at school, end up in prison or be unemployed in later life.”

The Prime Minister also announced that in future civil servants will have to assess the impact of legislation on families as well as the nation’s finances.

If a policy is judged to be detrimental to communities, it will be ruled as unacceptable as a proposal which is deemed unaffordable.

Speaking in Milton Keynes, he said he wanted his political career to be judged as much for his success in helping society as for his Government’s drive to restore the public finances and tackle the deficit.

“As our debts are paid off, this is what I want to endure as the lasting legacy of this administration,” he continued.

“Helping to build a society where families and communities are stronger, where our nation’s well-being is higher, and where all these things are accepted as central, not peripheral aspects of what modern governments should hope to achieve.”

He added: “Don’t think that I’ve forgotten about our pledge to make this country the most family-friendly in Europe.

“For too long, government policy has been made without enough understanding of the things I’ve been talking about today – family, community, relationships.

“When it comes to decisions about how and where to spend money, how policies are designed and implemented, how reforms are carried out government has sometimes seemed to carry on oblivious to the fact that we are human beings, behaving in ways that ministers and officials can’t possibly plan or predict.”

Meanwhile, Labour leader Ed Miliband has said while he is “pro-commitment” he also believes that stable families come in “different forms”. He was speaking ahead of his own marriage to long term partner Justine Thornton on Friday.

“I am pro-commitment, but I think that unlike David Cameron, I am not going to say that those families that aren’t married are automatically less stable than those families that are,” he told BBC Breakfast.

“Marriage is a good institution, it is right for me and Justine, but the thing that really matters to people is stable families and they come in different forms.”

He added that he and Ms Thornton had “always planned” to get married and tying the knot on Friday felt like the “right time” for them.

“I have always said … I am not going to get married for political pressure, I am going to get married at the right time for me,” he said.