Leading article: An index of happiness is at least a worthwhile endeavour

It was the 18th-century philosopher Jeremy Bentham who first popularised the notion that politics ought to aim at promoting "the greatest happiness of the greatest number". The problem his followers hit upon was working out a way to measure something as subjective as the feeling of what it is to be happy – and how to weigh the happiness of different sections of society against one another in the trade-off that is modern politics.

Even so, the notion of an index of well-being has tempted politicians ever since. The last to try it in Britain was Tony Blair who held "life satisfaction" seminars and commissioned various studies before concluding that happiness changed shape like mercury and slipped through the fingers. More recently, the French President, Nicolas Sarkozy, asked two Nobel economists, Joseph Stiglitz and Amartya Sen, to come up with a way to measure well-being. Now David Cameron has asked the Office for National Statistics to do the same.

It is easy to mock the notion. There is something of silly frivolity bound up in the word happy. Mr Cameron is attacking the idea that economic and material success is the most important thing in life, cynics will assume, only because he knows he is a prime minister doomed to be unable to deliver either at a time of public spending cuts, increased unemployment, home repossessions and ever more unaffordable education.

Yet there is something attractive in the idea of acknowledging that there is more to life than money. Britain's story over the past 50 years has been one of ever greater material wealth – but with happiness levels in steady decline. Britons are less happy than in the 1950s, despite the fact that we are three times richer. The proportion of people saying they are "very happy" has fallen from 52 per cent in 1957 to just 36 per cent today. All the studies show that, above an average income of about £10,000 per head, richer societies are no happier than poorer societies. They also show there is a link between happiness and health.

For Britain to become a happier nation, economic growth should cease to be the over-riding priority of government. But the big question is what else needs to be prioritised, and how. Research suggests that a number of factors interrelate to make us happy. At the top always comes the quality of personal and family relationships; marriage adds an average seven years to the life of a man and four to that of a woman. Next comes work, which brings both purpose and comradeship. Another is a sense of having a meaning to life, which is perhaps why religious people routinely come out higher in happiness tests. Yet another is people's sense that they can trust one another; there is a clear correlation between levels of mutual trust and happiness which are, for example, both high in Scandinavian countries in contrast to Britain and the US, which are more highly individualist and where the number of people who believe that "most other people can be trusted" has halved in the last 50 years.

If happiness is unmeasurable some elements of it are self-evidently not. The least happy people in our society are people with a record of mental illness; improving the therapies available for them is something well within the scope of political planning. The task of the Office for National Statistics is to consult the public and then develop measures based on what people say matters most to them. That is a worthwhile endeavour. Of course it will never be possible to compile a comprehensive measurement of the nation's happiness. But the attempt should throw up enough components to be of real value.