Britain’s broken society is all around us. It can be seen in the youths roaming the streets looking for trouble, the children getting hooked on drink and drugs, the emergence of a society in which family breakdown becomes the norm, and the chronic waste of resources and potential.

The broken society intrudes on our comfortable lives, sometimes brutally. John Monckton, a City banker, was killed in his own home in Chelsea by two thugs who had grown up on a life of drugs and crime. Lucy Braham was murdered in Harrow by a drug-crazed university dropout who, in her family’s own words in court, “descended from the gutter into the sewer”.

Iain Duncan Smith, the former Tory leader, last week presented the most comprehensive assessment of the problem. The statistics his Centre for Social Justice assembled for the Conservative party’s policy review make sober reading. Despite rising prosperity, more people live in severe poverty than in 1997; 3.5m are on benefits that place no requirement on them to work; 350,000 children have drug-addicted parents and 1m parents who are alcoholics; 10% of children leave school with no educational qualifications. The link between this failure and crime is powerful; 73% of young offenders admit to no academic attainment.

Mr Duncan Smith has travelled the country seeking out the worst examples. In Glasgow, which has 70% of Scotland’s most deprived areas, 50% of households have no earned income and life expectancy is as low as in many Third World countries. Lives are blighted by drugs, alcohol, crime and violence; the cycle of deprivation goes round, destroying successive generations. Glasgow may be the most extreme example but there are mini-Glasgows in every British city and, increasingly, in smaller towns.

What can be done to break the cycle that entrenches so many in this underclass? Mr Duncan Smith’s proposals have been characterised as presenting marriage as the solution to all society’s ills. In fact, while the evidence is strong - half of cohabiting couples break up by the time their child is five, compared with one in 12 married couples - he would emphasise that what matters is stable, long-term relationships.

There is a serious bias in the system against such relationships. This applies to everything from welfare benefits, tax credits and entitlement to council flats, through official advertisements on milk cartons warning single mothers that they could be guilty of benefit fraud if a partner has moved in. But Mr Duncan Smith’s diagnosis and recommendations go much further. There is no magic bullet for mending a broken society but a series of steps, some small, some expensive, none easy. By the age of three, a child is marked out for educational failure, crime and addiction. This can be stopped only by early intervention, such as the successful schemes that have run for 30 years in Baltimore in the United States.

What about the long-term unemployed, the Neets (not in education, employment or training) and the able-bodied “incapacitated”, who could work if given the opportunity? Australia’s Job Network uses private sector companies and charities to get people into jobs and ensure they stay in them, paying by results. Britain’s public sector-led employment service produces a revolving door; nearly 60% of those claiming jobseekers’ allowance have been previously unemployed. Hundreds of thousands more are allowed to rot on incapacity benefit at public expense.

Finding work for them and helping such people maintain stable relationships are the key. If the prime minister was as inclusive as he proclaims, he would put Mr Duncan Smith in charge of leading the assault on “breakdown” Britain. David Cameron must push the government hard on these issues and pledge to introduce real change when in power. The test for the Tories is whether they can force Labour to confront their agenda.