In February 2007, before becoming Britain’s prime minister, David Cameron said:

Sometimes a piece of research is published which goes straight to the heart of the national debate – it holds up a mirror to the whole of society and makes us see ourselves as we really are.

That happened this week. On Wednesday, Unicef published a report entitled “An overview of child well-being in rich countries”. It brings together comparative research on the material, educational and emotional state of childhood in 21 developed nations.

Britain comes bottom of the list.

Of course we can argue about methodology and the timing of statistics, but to do so is to miss the big point. This report shows that our society is deep trouble.

I am an optimistic person. I love this country. It’s a great place to live, a great time to be alive, and I am enormously positive about the future. But sometimes I simply want to despair – and this is one of those moments.

Ten years after the current Government was elected on the promise to end child poverty and make education its number one priority, Britain comes 18th out of 21 rich countries on material wellbeing, and 19th out of 21 on educational wellbeing. According to the report, British children are among the poorest and least educated in the developed world.

But that is not the worst of it. We come at the very bottom – 21st out of 21 – on three other measures which, to me, are even more important.

First, we come bottom on ‘subjective wellbeing’ – how children themselves rate their lives. Put another way, we have the unhappiest children in the developed world.