Why is there so much unhappiness in the UK?

I've noticed in the last 5 years or so that so many people are suffering depression, anxiety and general unhappiness. Now there's a report that the UK has the most unhappy, unhealthy and unsafe children in the developed world. It's not like the UK is a country that suffers as much poverty, famine, war and stuff that makes life incredibly hard in other parts of the world, so what's going on?