Is Britain a socially liberal or socially conservative country? In one respect the question is meaningless, because the answer will depend on personal perspective. To the radical libertarian, Britain will probably always seem like a hopelessly conservative nation, just as to the extreme reactionary it will resemble a sink of moral laxity.

But the annual British Social Attitudes study, released today, does, at least, help us understand the direction of travel. In 1983, when the first British Social Attitudes survey was conducted, 62 per cent of those questioned regarded homosexuality as "wrong". Today, the proportion of the public who admit to disapproving has declined to 33 per cent.

There has been a marked liberalisation of attitudes towards marriage too. Today, 14 per cent of people strongly believe that couples who have children ought to get married. In 1989, that view was held by 25 per cent of the public.

Attitudes on drugs have followed a less linear path. In 1993, 67 per cent thought cannabis ought to be illegal. In 2001, that had fallen to 46 per cent. But it has since climbed to 58 per cent today. And only 4 per cent presently believe the drug should be legalised. Another interesting finding of the survey is that more people are willing to describe themselves as "Conservative". This is perhaps a reflection of the achievement of David Cameron in changing public perceptions of his party, which, before his leadership, tended to be associated with social intolerance.

But politicians need to handle social attitudes with care, especially when it comes to drawing up public policy. The decision of the Home Secretary, Alan Johnson, to dismiss Professor David Nutt, the head of the Advisory Council on the Misuse of Drugs, for criticising the Government's decision to reclassify cannabis ought to have been popular in the country based on a crude reading of these trends. But many, in fact, felt it made Mr Johnson look as if he was incapable of dealing with dissent from an advisor, thus creating an impression of weakness. Meanwhile, the increasingly relaxed attitude of the public to cohabitation poses a dilemma for the Conservatives, who are committed to creating a new marriage tax break.

In the end, confident and successful politicians lead, rather than simply follow, public opinion. They are not bound by prevailing social attitudes when devising policies, but help to shape them. It is important to understand how attitudes change. The authors of this survey suggest that people in their 60s appear to have become more tolerant about cohabitation because of their personal experience of becoming a grandparent to a child born outside of marriage. Their attitudes are shaped by what they see and experience in their daily lives.

The social reforms of the Home Secretary, Roy Jenkins, in the 1960s were not popular at the time, but they helped change attitudes towards divorce and abortion over the decades. It has been a similar tale with New Labour's record on promoting homosexual rights, from the age of consent to civil partnerships. This programme has coincided with a general increase in tolerance towards gay people. The same relationship can be seen between legislation to protect ethnic minorities from discrimination and public attitudes towards racial difference.

What this survey helps to show is that a nation's social attitudes are a journey, not a destination. Political leaders need to be prepared to chart a course, rather than merely be carried by the tide.