Labour leader Ed Miliband (pictured) is set to marry on Friday, but it seems he doesn’t want it to be an advert for the institution of marriage.

Instead, he told the BBC that marriage does not ‘automatically’ make families more stable. He’s right about that, but on average marriage is much stable than cohabitation and that’s the point Miliband misses. After all, how many things in life are automatic?

Mr Miliband said: “I am pro-commitment, but I think that unlike David Cameron, I am not going to say that those families that aren’t married are automatically less stable than those families that are.

“Marriage is a good institution, it is right for me and Justine, but the thing that really matters to people is stable families and they come in different forms.”

Two points arise. Firstly, if marriage makes no significant difference, why is Mr Miliband entering into the institution? Presumably it’s just a personal choice.

He says that marriage “is a good institution”. But if it has nothing to do with stability, and commitment, as compared to non-marital families, what is so good about it?

Secondly, it should be noted that Mr Miliband is engaging in some rhetorical sleight of hand when he suggests that Prime Minister David Cameron says that married couples are “ automatically less stable” than non-marital couples.

Mr Cameron hasn’t said that, and nor does any serious pro-marriage person claim that marriage “automatically” makes a union more stable. Of course they don’t, anymore than poverty automatically leads to bad outcomes for poor people.

However, on average, married couples stay together (i.e. are more stable) longer than cohabiting couples. According to the British Millennium Cohort Study, only 10pc of married couples will have broken up by the time their child is five, compared with 25pc of cohabiting couples.

Only 35pc of British children born into a cohabiting union will live with both parents throughout their childhood, compared with 70pc born to married couples.

So if Ed Miliband values stability and commitment, then by his own logic, he should value the institution of marriage.