David Cameron will welcome a proposal this week to hand tax breaks to married couples as he seeks to make the family a key dividing line with Gordon Brown.

New tax and benefit payments to support marriage are among options included in a policy report by Iain Duncan Smith, the former Tory leader, to be published tomorrow, The Times has learnt. In response Mr Cameron is expected to say that the tax system should “affirm” marriage, as in every other large European country, and say that family breakdown in Britain is “extreme”.

The Tory leader will, however, emphasise that restoring the institution of marriage is a long-term aim and that single parents and unmarried couples must in the meantime be given more help to bring up their children.

The Social Justice Task Force led by Mr Duncan Smith makes recommendations across a broad sweep of policy, including proposals on addiction, debt and volunteering. It is, however, the section on supporting marriage, which includes the options of tax breaks, that will attract the most attention.

Tory strategists have decided to make the family a key battleground of the next election. Mr Cameron said yesterday that there was a gulf between the two main parties on the issue of social breakdown. “It is not now necessary in the same way to mend Britain’s broken economy, but it is absolutely necessary to mend Britain’s broken society,” he said.

In an early warning of potential pitfalls ahead, he appeared to accept that the unmarried would be worse off by comparison. Speaking on the BBC One Sunday AM programme, he said: “I think [marriage] is an important institution, it should be recognised and that would be a benefit.”

Single-parent campaigning groups served notice immediately that they would strongly oppose any proposal to discriminate against the unmarried. “Tax incentives for marriage are not untried policy in Britain,” a spokesman for One Parent Families said. “Tax allowances for married people existed throughout the 1970s and 1980s, which saw a massive expansion in divorce rates.”

Other proposals contained in Mr Duncan Smith’s report include making drinkers pay up to £400 million a year extra in tax to fund tough new treatment for drug addicts. The tax would add about 3p to a pint of beer, 15p to a bottle of wine and 25p to a bottle of whisky.

“We think that, as alcohol has its consequences, it is time for us to look at readjusting the price to bring it back in line with pricing that existed on alcohol before.” His task force also wants cannabis upgraded to a class B drug and heroin users encouraged to go “cold turkey” rather than be treated with substitutes such as methadone.

The report will claim that the Government’s drug policies have become part of the problem and call for an end to “nonjudgmental, politically correct and scientifically inadequate” school programmes. In its interim Breakdown Britain report last year, the group gave warning that severe debt, drug addiction and the breakdown of the family were creating a growing underclass.

In the meantime, Mr Cameron faced criticism over his calls for a referendum on the proposed EU reform treaty from two Tory grandees. Kenneth Clarke, the former Chancellor, said that referendum demands had “an inner absurdity” and argued that moving away from Euro-scepticism would boost Tory electability.

Speaking on the GMTV Sunday Programme, the strongly pro-European Mr Clarke said: “One thing that will make a Conservative Party electable . . . will be if we continue to dilute this absurd, extreme Euro-sceptism that swept over the party in the last ten years.”

Lord Hurd of Westwell, a former Foreign Secretary, credited Mr Cameron with “draining the poison” from the issue, but said that a referendum was unjustified.

Lord Hurd told GMTV that referendums should be reserved for “the most extraordinary earthquakes which are proposed”, adding: “I don’t think there is anything in this treaty, insofar as we can see it now, which actually justifies that.”

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