15/10/2013 07:57 BST | Updated 14/12/2013 05:12 GMT

Don't Judge My Family, Mr Cameron

"Mummy, are you and daddy married?"

Not a question I've yet had to field from my three year old. But one I am expecting. And one of the few things that might actually lead to me getting married. So far, despite being with my partner for over fifteen years, marriage just hasn't felt particular important or necessary. We are committed and that is enough for me. But if either of my sons really wanted us to take this step then that would probably be very persuasive.

What I don't think I will be getting married for is a £3.85 a week tax break. And neither will many others, it seems. Even the Prime Minister admits that the marriage tax break isn't going to encourage anyone to get - or stay - married.

Instead the policy is about 'sending a signal'. A signal that marriage is best. As a member of the Don't Judge My Family campaign I'm keen to send Government a signal right back: great families come in all shapes and sizes, and government has no place in promoting one type of family model over another.

In reality the marriage tax break will be worth £200 a year and will go to only a third of all married couples: those with a breadwinner and a homemaker. That tells you everything you need to know about the kind of families this government wants to promote. People up and down the country are outraged that in 2013, the government feels it has a right to judge.

And all this judging is going to cost a lot of money. £700m a year. That's more than the cuts to SureStart (£430m), more than the cuts to EMA (the educational maintenance allowance) (£560m) and more than it'd cost to reverse the bedroom tax (£470m). In these difficult times, the government should be helping all families not judging them.

Discussions of tax breaks for married couples often end up about children. But again, it is poorly targeted to help children. Over a third of those who benefit are pensioners, whose kids will have flown the nest. In fact the tax break will go to only 17.4% of all families with children.

The allowance won't go to the one in four families headed by a single parent. Widows and widowers lose out. Nor does it go to couples where both work to make ends meet, or those where neither are able to work. It doesn't go to those who have very happy stable relationships (like mine) but choose not to marry. Or those who are fleeing domestic abuse. To add insult to injury, an adulterer who marries again would get the £200 whilst the person left "holding the baby" loses out.

So it's a married couples tax allowance that only benefits a minority of married couples. This could get kind of confusing. And so it would appear because David Cameron, rather embarrassingly, stands accused of slipping up in Parliament about just who would benefit. Perhaps even he got confused about just how limited a policy it actually is.

But what about the claims that 'marriage matters'? That it is intrinsically important in and of itself. The IFS agrees that children born to married couples do better in both cognitive and social outcomes than those born to cohabiting parents. However this is explained by the fact that cohabiting couples often have lower educational qualifications and lower income than married couples. The research shows that these factors explain why those children have lower outcomes. There doesn't seem to be any evidence that getting people who are cohabiting down the aisle would increase their qualifications or income and therefore their children's outcomes.

So the claim that this is about supporting families and children doesn't really stack up. Yet this policy will cost around £700m a year: in the toughest times for a generation, David Cameron can find over half a billion pounds to spend on promoting his fantasy fifties family whilst slashing budgets elsewhere.

There are so many ways scarce public funds could be better spent. This is why Don't Judge My Family has launched a call for evidence from academics, charities and members of the public to tell us how they'd spend £700m on relationships, families, or giving kids the best start in life. We'd love to hear your views.