Marriage in Britain is in danger of becoming an exclusive middle-class institution unless action is taken to bolster it, David Willetts, the shadow cabinet member responsible for the family, says today.

Speaking to the Guardian, Willetts said it would be "extremely dangerous if marriage became something only for the affluent elite" and that the rate of family break-ups was a disaster for children.

The Conservatives are due to publish their ideas on the family in a discussion paper arguing the state and the voluntary sector can do more to help fathers in relationships, especially at the birth of the first child, frequently a point where couples drift apart and separate.

The party will also back recognition of marriage in the tax system, as well as providing relationship advice at civil marriage ceremonies.

The green paper will propose changes in the law to make it easier for grandparents and fathers to stay in contact with children when marriages break up.

Willetts insisted there was measurable evidence to show that married couples with children, as opposed to cohabiting couples, stayed together longer to the benefit of children.

"The aspiration of marriage is becoming harder to achieve. Instead of it becoming just what you do in your 20s, it has become like scaling Mount Everest, a sort of great moral endeavour – and something that requires a lot of time and money. We think we need to ease some of the pressures," he said.

"There is quite a lot of evidence coming from America about how we are in danger of heading towards a society where middle-class people get married and people on low and erratic incomes don't get married, and that in turn leads to a divergence of a whole host of other outcomes.

"In my view it would be extremely dangerous if marriage became something only for the affluent elite and that is what will happen, unless we try to get some kind of policy that restores it as a more widespread institution as we had in the past."

Research from Essex University shows that less educated women born after 1960 have a divorce rate 30% higher than that of the better educated. They are also more likely to have a child outside a live-in partnership. The figures and trends are even more pronounced in the US.

One explanation for the middle-class bias towards marriage in the US, Willetts said, was the fact that there were fewer eligible working-class males, owing to deskilling of societies.

He insisted that the Tories were not returning to a back-to-basics preaching agenda, and recognised that some marriages will fail.

Owing to budgetary pressures it was unlikely that recognition of marriage in the tax system would appear in the Tories' first budget, but it was important to establish the principle, he said. Recognition of marriage in the tax system would bring Britain back into the mainstream of European society, he argued.

"If you look at the analysis of the way in which most tax and benefit systems work, it looks as if the group that gets the raw deal in Britain compared with other advanced western countries is one-earner couples.

"That is the way in which the combined effect of our income tax and our tax credit work. The second adult being invisible in the tax credit system is very odd indeed," Willetts said.

Latest UK evidence shows marriage rates are at a historic low, with only 270,000 people married last year compared with 480,285 at the peak in 1972.

Willetts defended his belief that marriage helped couples stay together to the benefit of the child, saying: "Any society in which something as massive as this institution of marriage with a deep history, with roots in its culture, with public recognition, where it didn't affect behaviour would be very odd indeed."

He insisted: "I think there are things that have gone deeply wrong with our country. The rate of family break-up is a disaster for children."

Current evidence suggested that people divorced too readily, but Willetts admitted that his party could find no way to make divorce more difficult in law.

The green paper will propose home nurse visits for new families with greater emphasis on help for the father, and relationship guidance at the time of a civil marriage similar to that given by a vicar. He would also like to spread the model of the Bristol community family trust that provides relationship courses to 30% of new mothers in the city.

In cases of relationship breakdown, Willetts proposes that fathers should be given access to tax credits if they are looking after the child more frequently than the mother, and grandparents should be automatically considered for placements if both parents are not deemed suitable to bring up the children. Grandparents should also be considered for access to the child following a divorce.

He said: "We do not think law custom or practice has kept up with the transformed role of grandparents." Surveys showed that one third of teenage girls say they can talk to their maternal grandmother about questions they wouldn't feel comfortable talking to their parents about.

He also proposed that children's school reports should be sent to fathers as well as mothers in cases of breakdown. "You don't have to dress up in a Batman's costume outside Buckingham Palace to think there are circumstances where law and practice lag way behind the reality."

The green paper will say greater pressure is being placed on the family because of a decline in trust in other adults.