The UK’s deputy Prime Minister and Liberal Democrat leader Nick Clegg has attacked in rather odd terms proposals to give a modest tax break to married couples.

In a speech a few days ago he said: “We should not take a particular version of the family institution, such as the 1950s model of suit-wearing, breadwinning dad and aproned, homemaking mother, and try and preserve it in aspic.”

Mr Clegg also opined that couples married for love, not to “get some cash back from the state”.

As a liberal, he added, “I think there are limits to how the state and government should try to micromanage or incentivise people’s own behaviour in their private lives.”

Of course, talking about the “1950s model of suit-wearing, breadwinning dad and aproned, homemaking mother” is a pure red herring. No-one is trying restore that version of marriage.

As to his comments about people marrying for love, again, no-one is suggesting that people get married for State cash. Many couples want to get married, but feel they cannot. The Tory proposal is about encouraging such couples to get married.

The proposal is also about something more important than the sum of money involved (which reports suggest will initially be small). It is about making a cultural statement that marriage is something worth preserving as a social institution.

The reason is that most of the Tory leadership has come to acknowledge that marriage is the family structure in which children usually fare best. The evidence for this is now incontrovertible. Children raised by their married, biological parents fare better emotionally, economically and educationally compared to those raised in other family structures.

This is true even when factors such as poverty, race and other forms of social exclusion are taken into account.

A new paper from the US think tank, Child Trends, further bears this out.

Which brings us to Mr Clegg’s assertion as to the limits of the State in terms of ‘micromanaging’ or incentivising people’s behaviour in their private lives. For a start, the decision to raise or not to raise your own children together is not an entirely private decision. It has social consequences.

For example, estimates for the costs created by family breakdown each year to the UK Exchequer range between £20bn to £40bn. So how can the decline of marriage (and in Britain it has declined very sharply) be purely a private matter.?

Clegg did not object last year when the Chancellor George Osborne (who also shares his scepticism about giving special tax treatment to marriage) implemented a budget which hit single income couples far harder than double income couples.

How did that not constitute the state “micromanaging” people’s private lives?

The truth is that every tax regime is involved to some extent in incentivising (or disincentivising) people’s behaviour. The choice that a Government is whether those incentives should be in favour of the family structure which helps children the most, or alternative family structures. For some reason, Mr Clegg seems to favour the latter.