The French are often accused of being grumpy and dismissive.

But Britons and Americans are also hardwired to be miserable, scientists claim.

Despite stable governments and good economies, those living in the UK and US will never be as happy as people in other nations, because they are simply born more miserable.

They are genetically programmed to be less cheerful than the Danes, for example, who top the list of the happiest nation.

And scientists at the University of Warwick discovered it all comes down to a gene which regulates levels of the hormone serotonin in the brain.

Short forms of the gene inhibit levels of the hormone, which can invoke depression.

Meanwhile those with longer forms of the gene are more likely to be happier, as a result of higher levels of serotonin in the body.

Researchers discovered people from Denmark have the longest form of the gene, and as such topped the happiness chart.

But Professor Andrew Oswald said it could be worse, we could be French - the nation with one of the shortest forms of the gene, which may explain their reputation for being grumpy.

Annual tables of national happiness ratings, compiled by organisations across the world, tend to rank Denmark at the top, along with nations including Panama and Vietnam.

They use factors ranging from job satisfaction to economic progress, health, wealth and education standards, along with weather, war and political stability to judge nations.

Scandinavians do well as their health is good, they are educated to a high standard and they earn more. But warm weather countries can do well too.

Some wealthy Western countries fare less well because there are big divides between rich and poor or they have high unemployment rates or less job satisfaction for instance.

But according to Professor Oswald, many of these may still be miserable even if they are earning a fortune, basking in sunshine and living to 100.

His findings from 131 countries for the ESRC Festival of Social Sciences, found genetics to be the most important factor but not the only one.

Those who are either young or old tend to be happiest rather than those who are middle aged.

Those who are slim are happiest, with obesity levels in some developed countries making them less happy as nations.

And being married, in a job and well educated can also be a contributory factor.

Professor Oswald, said: 'Intriguingly, among the nations we studied, Denmark and the Netherlands appeared to have the lowest percentage of people with the short version of the serotonin gene.'

He added that many individual Americans were happy but they tended to be descended from immigrants who came from countries like Denmark in the first place.

He said: 'There was a direct correlation between the (US) individual's reported happiness, and the levels of happiness in the country their ancestors had come from.

'Our study revealed an unexplained correlation between the happiness today of some nations and the observed happiness of Americans whose ancestors came from these nations.'