WHILE Cabinet ministers debate whether or not the Government should endorse marriage, everyone agrees that the existing benefit system works against those who choose to tie the knot.

There is growing evidence that couples negotiating their way through an increasingly complex system of tax credits and benefits are finding that they are better off living apart.

The Daily Telegraph revealed earlier this year that the thousands of couples who pretend to live apart so they can claim larger lone-parent benefits are costing the taxpayer more than pounds 400 million a year. The Institute for Fiscal Studies has estimated that many couples will be more than pounds 50 a week worse off if they stay together than if they separate.

Take an unmarried couple with two children where the father earns pounds 15,000 a year and the mother another pounds 5,000. If the couple live apart, the mother is entitled to nearly pounds 7,800 a year in tax credits and benefits.

However, if they stay together and claim as a couple, they will only receive pounds 2,300 - a penalty of more than pounds 5,400.

Critics claim that the perverse incentives to live apart - or pretend to live apart - mean that few couples on benefits will ever consider marriage, not least because it may make it more difficult to persuade benefit officials that they are living apart.

Many Labour MPs argue that singling out married couples for extra help discriminates against lone-parent families.However, David Ruffley, the shadow welfare reform minister, said last night: "Our work on reforming the benefit system has exposed that there are poor incentives to bolster marriage. The tax and benefit system needs to be rebalanced to support marriage.''