Is happiness, which we think of as fleeting, a realistic state to which to aspire?
I think happiness is what people most care about. They want to know how happy their child is. They want to know whether they’re happy in their work, they want to know whether they’re happy in their marriages. It’s not that it’s happiness or nothing. It’s somewhere on the scale. And we want to be higher up the scale. We want everybody to be higher up the scale and that’s to my mind the definition of a good society.

You write in the book about the attempted suicide by your father (the distinguished psychoanalyst John Layard) before he met your mother. How formative was that knowledge in your young life?
Well, I was aware of it because I used to feel the dent in his head where the bullet had lodged but it wasn’t what made me think about people’s unhappiness. What did interest me in mental health was not my father but his patients and the fact that my father was able to help them. That I think was where my interest in mental health came from rather than from any kind of angst.

Given your interest in your father’s patients, what directed you to economics?
I did think of becoming a psychiatrist but I in fact became a schoolteacher. I went to the LSE for evening classes to broaden my education and after that I became the research officer for the Robbins committee on higher education [which led to the expansion of universities]. I was at once struck by the difficulty of making the case for why more money should be spent on one thing rather than another. And I discovered that there was such a thing called cost-benefit analysis and I decided I should become an economist, because that had the merit of at least trying to develop a rational basis for choosing priorities for government spending.

You argue that happiness should be a key metric, like GDP, in assessing a nation’s performance. Can happiness be reliably measured, given that it is a subjective quality?
It is a subjective quality and that’s why it matters, because how people feel is their deepest reality and it’s the way we should think about the quality of the person’s life. How is their life as they themselves experience it, not as we think it might be. The standard way to find out is to ask people: overall, how satisfied with your life are you on a scale of 0 to 10, with 10 extremely satisfied and 0 extremely dissatisfied?

It seems inherent in human nature to believe that we were happier in the past. But is the UK more or less happy now than in years gone by?
This is probably one of the best periods the human race has been through. We know quite a lot about that from evidence. In the US, where we have the longest time series, happiness has been pretty much flat. In the world as whole it’s risen since 1970. In some countries it hasn’t. Britain has risen slightly. We’re not at all in the business of saying this is a terrible period. But there are some people having a really hard time in their lives and everybody could have a better time.

We tend to focus on economic status as the key to the good life, but how much bearing do wealth or poverty have on happiness?
Less than 2% of the huge variation in happiness within our society is explained by variation in income. By far the most important single factor is mental health. Physical health also matters. The other huge influences are human relationships – in our family, whether we have a partner and whether we’re happy with the partner. Also very important is the quality of work and of course whether we have work, but in particular how we’re getting on with our colleagues at work. And finally the community – are we living in a friendly community where we feel safe?

You speak about the importance of increasing the happiness of others. But the law of unintended consequences tells us that the road to hell is paved with good intentions.
That’s a very good point and it’s one reason why we should be using whatever evidence we have on the things that are really important to people. For example, if we take the school teaching profession we know that the most important predictor of whether a young person will be a happy adult is not the grades they get but whether they’re happy at school. It would make a huge difference if we could get away from the focus on exams as the main purpose of education, which sets people such a burden of responsibility to themselves.

A happy society has to be explicitly aimed for, you say. It will never come as a byproduct. Why?
Because it’s so easy to get diverted into things that are more obviously measurable. So what has happened is that because income can be measured, income has become the totem pole at the level of the country and the GDP. This is the thing that politicians feel is critical – how they deal with the economy – but we know that the way people vote in elections is not influenced as much by people’s economic status as satisfaction with all other aspects of their lives.

Immigration, you say, is a cause of anxiety. Can we maintain the trend towards greater migration and also become happier?
The story of migration is that in the end the migrants become the natives. And in that sense zero migration is a ridiculous idea. So if people want to come in we should up to a point welcome them. But if the speed is too fast it creates tensions and therefore we have to have controlled migration. There will be no other way of sustaining a harmonious community. It’s a matter of balance.

You make reference to the link between levels of unhappiness and the growth of populism. What is that relationship?
The general point, which has been confirmed by studies of European elections since the 1970s and studies of the Trump vote in the US, is that the higher their level of life satisfaction, the more people are likely to vote for the existing government – or parties currently in power. This explains more of the variation in election outcomes than the economy does. So people’s votes reflect more how they feel in terms of non-economic causes of their enjoyment of life than the economic causes. This is why the case for government making wellbeing their target is also based on their own self-interest. If it wants to be re-elected it should not just go for economic growth but all the things that matter to people.

And what is the specific relationship in terms of populism?
First it’s true that less happy people are more likely to vote populist. But the second fact is that in European countries, except for Italy and Greece, there hasn’t been an increase in the number of unhappy people. In the US there has been an increase. So you’ve got to find in Europe some other explanation of populism. I think there are four factors to explain its growth. One, the long-term trend towards reduced deference, but two is the fact that the elite discredited themselves greatly by allowing the 2008 financial crisis to be generated and to a degree mishandled afterwards. Three, I think immigration is an issue – many people feel that their interest is not being considered.

But I think that the main reason for this sudden change is social media. When you talk to people face to face you have to moderate your language. But this economic method of communication has led to people feeling much less constrained by the normal rules of etiquette, and people have become quite wild in their expressions of their frustrations. To sum up, there has not been a big increase in discontent but there has been a complete change in the way people express it. They feel entitled to disrespect the elite and they feel entitled to do this on social media and in voting.

Should the UK follow New Zealand’s lead and formally target wellbeing?
Definitely. We have a great opportunity now we have a new government that’s rethinking its priorities. There are three countries that have adopted wellbeing as their targets recently – New Zealand, Scotland and Iceland, all with female leaders. Now Boris Johnson has the chance to become the first male prime minister to make wellbeing his target. That would be a great moment if Britain gave that lead to the world.

Happiness varies from hour to hour, but there tends to be an underlying trend in our lives. In your own life, do you think that there has been a great deal of variation or have you remained roughly consistent?
Of course it fluctuates from day to day and month to month. I think on the whole that I’ve been lucky and have had a happy life. In the past 20 years since I’ve been writing about all this, I have gained a lot from what I’ve learned, both in terms of being more aware of other people’s feelings but also in being better able to distance myself from the negative thoughts and feelings that all of us have from time to time.