Leading article: A deceptively modest tax break

In setting out the details of his promised tax break for married couples, David Cameron has characteristically boxed clever. He has established the principle – that marriage and civil partnership will be rewarded – while ensuring that the benefit in practice will be tiny.

One reason for the small sum on offer, of course, is the parlous state of the public finances. But another is surely the controversial nature of the concession. Rewarding marriage does not command universal support, even among Conservatives. Elsewhere it provokes scorn, resentment, or even anger. Labour opposes it on the rather disingenuous grounds that it amounts to "social engineering" – as though policies generally, theirs included, have no such intent. Labour had also said that such a break would tend to favour the rich and penalise the poor – which may be why higher-rate tax-payers have been excluded.

For the Liberal Democrats, Nick Clegg's dismissal was sharper. He described it as "patronising drivel" from bygone days. We agree: the decision to marry or not is a personal one. It is, and should remain, nothing to do with the tax-man. For the state to reward marriage financially throws up many anomalies and risks restoring social stigmas we hoped had been lost. In Britain, each of us is responsible for our own tax affairs, and it should stay that way.

Just because the Conservatives' proposals involve little money, however, does not mean they should be ignored. Here is a potential government not only wanting to send a moral message, but also shifting a basic principle of our tax system. Once a part of the personal tax-free allowance has been made transferable, an element of household, as opposed to individual, taxation has been introduced, which could presage full transferability if the public finances improve.

The plus of household taxation is that it more closely matches the means-tested benefits system. But the minuses are many: not only may some women be deterred from working, but the disparities between the tax treatment of married and unmarried households will grow. We should not be deceived. The implications of what the Conservatives are proposing go far beyond the initially modest bonus of £150 a year.