Iain Duncan Smith’s report on social breakdown is almost as long as the Alastair Campbell diaries, and deserves even more attention. It is the most important of the Conservative policy reviews so far: not because all its recommendations will be accepted, but because it addresses fundamental questions about what is wrong with Britain and the role of the State. It goes to the heart of what David Cameron means by social responsibility.

The report is about much more than the tax treatment of marriage. The scope is as wide as the Beveridge report of 65 years ago, on which it is modelled, and it is no less ambitious: addressing Mr Duncan Smith’s updated evils of family breakdown; addiction (drugs, alcohol and gambling); poor and failed education; and welfare dependency.

The thoroughly researched analysis is compelling about the interaction of these “evils”, and particularly that the cycle of disadvantage starts very early. That has been recognised by the present Government with its Sure Start schemes, and more recently its targeted help for at-risk mothers.

The central question is what can, and should, the State do? The Duncan Smith position, in line with Mr Cameron, is that government should have a view on our “broken society”, and cannot be completely libertarian.

“We have become far too tolerant of social failure,” as Mr Cameron said yesterday. But that leads into two tricky questions.

First, how far should the State set up a model of desirable behaviour? Politicians of all parties get themselves tangled in knots here. Labour ministers have set themselves against both legal activities and illegal ones – truancy, teenage pregnancy, binge drinking, smoking cannabis – but have backed more casinos.

Tories often deplore the nanny state, while advocating actions intended to strengthen the family. They are right that those who have experienced family breakdown are much more likely to fail at school, become addicted to drugs and have alcohol problems.

Statistically, a stable background is more likely to occur with married couples, but there are plenty of highly successful single parents. There is a fine line between saying that marriage is a good thing and appearing to discriminate: and public, even Tory, opinion is split on this issue.

Secondly, how far can the State itself produce outcomes? Mr Cameron’s mantra of social/shared responsibility involves government encouraging and allowing individuals and voluntary bodies to do good: for instance, by allowing parents and other providers to set up new schools with charitable status, akin to charter schools in the United States. Voluntary groups should be more involved in helping addicts and people back to work. The Duncan Smith report also suggests a host of tax and benefit changes: to reward marriage and put pressure on lone parents to work. Tax policy should be “a crucial element” in preventing a further rise in overall alcohol consumption, and preferably bringing it down.

There will now be a lengthy public and party debate on the report. This needs to be about much more than marriage and the tax system. If Mr Cameron wants to reassert his party’s One Nation traditions, he needs to define much more precisely the role, as well as the scale, of the State.

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