Cameron promises tax breaks to give families extra £2,000 a year

The Tory leader's radical plan is designed to end the benefits anomaly which penalises parents who stay together.

An estimated 1.8million families would be up to £2,000 a year better off under the proposals, to be announced formally next week.

And the £3billion cost would be met by a crackdown on workshy benefit claimants, including "aggressive" penalties for those who turn down jobs and the privatisation of welfare-to-work programmes.

Mr Cameron came out fighting after a week which saw Gordon Brown stage a series of raids on Tory territory by offering himself as a champion of traditional values.

"At the heart of a strong society are strong families, who live together and stay together," Mr Cameron tells the Daily Mail in an exclusive eve-of-conference interview with Allison Pearson.

In it, he also promises to "kill off" some of the "barmy" proposals put forward by the party's policy reviews, with a "bonfire" of ideas including higher taxes on alcohol, charges for supermarket parking and a cap on holiday flights.

The Tory leader will defy his critics by putting clear blue water between him and Labour on key issues such as tax, law and order and immigration.

But the focus on the family will be one of the centrepieces of the Tories' Blackpool conference, which opens tomorrow with him under pressure to reassert his authority amid fevered speculation of an imminent election.

He proposes to increase sharply the amount paid to couples who qualify for the Government's main in-work benefit - the Working Tax Credit - in what amounts to a landmark change in the way the state treats families with children.

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Family man: Cameron with wife Samantha

Under current rules, a single mother with two children under 11, working 16 hours a week on the minimum wage, has a net income of £487 a week, most of it tax credits.

To take home as much, a two-parent household on minimum wage would have to work 116 hours a week between them.

The "couple penalty" has been blamed for the massive levels of fraud which have discredited Mr Brown's flagship tax credit system, and what opponents claim is widespread social failure.

The case for tackling the problem was set out earlier this year in a study produced by former Tory leader Iain Duncan Smith.

Mr Cameron confirmed that its key recommendations will be at the heart of a family-friendly package in the next Tory manifesto.

He told the Mail: "Social breakdown is costing our country over £100billion a year in economic dependency, educational failure and rising violent crime.

"I believe that at the heart of a strong society are strong families, who live together and stay together, yet Britain has one of the highest rates of family breakdown in Europe.

"The crazy thing is that Gordon Brown's tax credit system actually penalises people who want to live together - sometimes by thousands of pounds a year.

"By getting rid of the 'couple penalty' we will encourage families to stay together not move apart.

"To pay for it we are going to move many more people who are out of work and living off benefits into work.

"That is good for them and right for the taxpayer."

The extra cash would be available to married or unmarried couples with children who qualify for Working Tax Credit, the means-tested top-up given through the wage packet to those on low-paying jobs.

Same-sex couples with adopted children or children from a previous relationship could also qualify, but couples without children would not.

Cutting Incapacity Benefit alone could easily pay for the scheme. It is currently paid to 2.7million claimants, at a cost to the taxpayer of £12.5billion a year.

Ironically, in a week which has seen Labour abandon its traditional concerns to focus on Rightwing issues, Mr Cameron's package is most likely to benefit families on low incomes who are traditionally more likely to vote Labour.

Opponents will question his claim that he can deliver significant reductions in the number of jobless benefit claimants, pointing out that they proved themselves to be fiercely resistant in the past to efforts to get them working.

In a candid and deeply personal interview, Mr Cameron reveals a sleek new look and, on the eve of what MPs say is a make-or-break conference for him, says he is ready to take on Mr Brown in a November election.

And he makes clear he will not accept some of the controversial proposals to have emerged from the policy commissions which have generated ideas for the party's manifesto, including charging for supermarket parking and a beer tax.

In another interview, Shadow Chancellor George Osborne dropped a broad hint of imminent action on death duties, saying: "Inheritance tax is an increasingly unfair tax that is hitting many, many families who are not super-rich."