Jeff Short spoke with Harry Benson from The Marriage Foundation, who says that the fact that more marriages are staying together, is good for teenagers' mental health.

Jeff: That's got to be the best kept secret ever, that the divorce rate is falling for those in the early stages of marriage. You would guess that if you were to speak to the average person in the street they would say oh no, people go into marriage and then they come off their honeymoon and then split up.

Harry: The difficulty here is we tend to conflate married couples with unmarried couples and everybody knows with both that some relationships work and some don't. What we tend to do is mix the two up in our minds and we see more couples splitting up and we think that must be due to divorce. But actually it isn't. Most of it is due to unmarried couples splitting up.

Just to give you an example: if you compare two typical couples who have a baby and follow them over the next 15, 16 years until their kids are sitting GCSEs, if they are married about a quarter will split up; if they were not married, about seven out of 10 will split up. That's the big difference.

There are other factors involved, education plays a part here. But by and large if you're married, you've made a decision about the future. People tend to stick at it and do well in it as well. There are horrible marriages out there, but the vast majority of them are doing really well.

Jeff: It strikes me, and you alluded to it, that then has an impact on the well-being of 13 to 15 year olds. That has got to be important because we're hearing so much about the need for better provision of mental health services among that teenage group, who are under the pressures of social media. Would you say, and I'm not trying to put words into your mouth, that that group might well enjoy a more rounded family life and that might be better for their mental health?

Harry: For sure, there's no question about it. There's been an enormous amount of talk in the press and in politics about how social media and smart phones have been influencing teenagers. And also how exam pressure has been influencing them.

The evidence we see and the research that we've done, suggests that the number one driver of teenage mental health, so whether you worry unduly about your situation and you're filled with anxiety, or you misbehave and mess around outside, those sorts of things tend to be associated more with family breakdown than anything else. For us, the evidence that we see suggests that family breakdown is the number one driver.

In theory, if family breakdown is reduced, which we now see that it has over the last 10 years, we think it will continue to reduce over the next 10 years, because the lower divorce rate is still filtering through the system. We think we will see a reduction in teenage mental health problems.

Jeff: And it makes good economic sense, because I've seen some figures that you have put out that family breakdown costs the taxpayer £51 billion a year.

Harry: Yes, and that will also fall, as fewer families split up.

That is only because the married families are doing better. This is not to do with unmarried families; it's very important that we make that distinction.

As fewer families split up you have less need for benefits, tax credits, universal credits, housing benefits, council tax benefit and all those sorts of things. Not to mention the legal costs that can be incurred, and the care system and extra health costs.

So yes, you're absolutely right, family breakdown falling because marriages are doing better, should have a knock on effect on social costs and also teenage mental health. Good news all round.

Jeff: It flies in the face of the homespun philosophy that people very often bring out, that you shouldn't stay together for the sake of the children.