Leading article: That was then. This is now

David Cameron, like every other public figure, is entitled to a past. When asked during the Conservative leadership campaign, he was entitled to refuse to answer questions about whether he had used illegal drugs as a young man. He is, in fact, only the second leading British politician for whom this issue has arisen. Paddy Ashdown once became cross and refused to answer the same question put to him by a student magazine. Tony Blair and Gordon Brown, on the other hand, have both said "No" (as did David Miliband when the question was put to him by a reader of The Independent last month).

That does not mean, however, that newspapers should refrain from publishing information about the pasts of public figures. Mr Cameron is entitled not to tell us, but when we find out about the early life of a man who aspires to lead the country, the public has a right to know.

As a proudly liberal newspaper, The Independent on Sunday does not believe that youthful experimentation with illegal drugs detracts from an MP's ability to legislate, or a potential prime minister's ability to lead.

Our revelation today that Mr Cameron was disciplined at Eton for smoking cannabis is bound to make headlines. We can predict the fury of parts of the Conservative Party and conservative press. It will be argued that public figures have a responsibility as role models. And it is true that there are dangers in presenting cannabis as harmless or socially acceptable. Doctors are increasingly concerned about the psychological impact of cannabis on a susceptible minority. But what matters is whether Mr Cameron can use his experience and that of those close to him to inform a credible policy. In this respect, he cannot be faulted. He has been brave in facing down his party's authoritarian instincts in advocating a harm-reduction strategy to deal with the problems of drug addiction. He advocates intensive - and expensive - rehabilitation for addicts as an alternative to prison.

There may be cynics who will say that our report today of Mr Cameron's drug-taking at school, and possibly at university, is part of a media management operation on behalf of the Conservative leader. It may be speculated that it is convenient for him to get this story out now rather than during the next election campaign, or to soften up the public for further revelations to come. Such cynicism would be misplaced. The fact that Mr Cameron got into trouble for smoking cannabis was discovered and confirmed by the journalistic endeavour of James Hanning and Francis Elliott, this newspaper's executive editor and Whitehall editor respectively. Their forthcoming biography of the Conservative leader promises a thorough and fair picture of a man who could be prime minister.

We take the view that Mr Cameron's use of illegal drugs before he became an MP has no bearing on his ability to discharge the responsibilities of high office. To those tempted to be censorious, we would urge calmness and a sense of proportion. We would remind them that Mr Cameron was at the time of the incident a 15-year-old child, and ask who has not done foolish things at that age?

Charles Kennedy's use of a legal intoxicant while a member of the House of Commons was rather more material than Mr Cameron's use of an illegal one many years ago. We believe that our view reflects the trend in public attitudes, and that if our report provokes a media frenzy it will be a relatively restrained one. The lesson of the battering that Mr Cameron took over drugs in the leadership election is that the public largely took his side.