The first glimpse of the truth often comes from someone inside the organisation involved. It may be passed to the press, an MP, a pressure group or a regulatory agency. But however formidable these bodies' investigatory skills, that initial inside information is crucial.

Reactions to whistleblowers - whether they act anonymously or speak out openly - are often ambivalent. The person we consider has performed a heroic public service will, in other eyes, be betraying the trust of colleagues or the institution. So let us acknowledge immediately, that blowing the whistle may sometimes be the wrong thing to do. How many of us would accept our own apparent failings being publicly exposed by a colleague who may have misread the evidence, or has made no effort to raise the issue with us first?

But when something is seriously wrong, when the public is put at risk, and when a conscientious employee has tried everything to remedy the matter from the inside, the issues become clearer. The overriding public interest may lie in protecting our right to be told, and the whistleblower's right not to be punished for telling us.

When the new Official Secrets Act was introduced in 1989, ministers resolutely rejected a public interest defence to allow the civil servant who may have released information, or the journalist who published it, to defend themselves on the grounds that the disclosure was justified.

The then Home Secretary, Douglas Hurd, repeatedly claimed that such a defence was without precedent in the criminal law. In fact, the precedents not only exist but are found in the Home Office's own legislation - notably the obscenity laws, which contain precisely such a "public good" defence.

The statute books are peppered with some 250 additional legal penalties for disclosing information. Many protect individual privacy but others criminalise officials for daring to disclose even safety information on dangerous products. Again, no public interest defence is available.

The contracts of both public and private sector employees increasingly contain gagging clauses, making the unauthorised disclosure of any information to anyone a disciplinary offence which could lead to dismissal.

Equally worrying is the trend for confidentiality clauses in out-of-court settlements. The victims of unfair dismissal, sex discrimination or dangerous consumer products may get their compensation - but only in return for a binding promise of silence. This may protect a negligent company's reputation. It also allows it to buy off the strongest claimants, undermining others by denying them the previous evidence.

Journalists sometimes risk imprisonment to protect their sources' anonymity - a basic requirement if those with evidence of wrongdoing are to come forward. Here the government operates a curious double standard. The legislation which allows us to see official information, from the Data Protection Act to the law opening up council meetings, all permit public authorities to conceal the identity of their sources. A similar principle applies during legal proceedings, where the identity of certain kinds of informants is often protected by public interest immunity certificates.

But when journalists argue that their sources too should be protected, the rules change. The Contempt of Court Act appears to allow journalists to protect sources in most cases. But it was shown to be near useless when, in 1990, journalist Bill Goodwin was held to be in contempt by the House of Lords for protecting his informant from a company who wanted it for no higher purpose than to punish the discloser and plug the leak.

Could whistleblowing ever be rendered unnecessary? A powerful Freedom of Information Act - which would expose information without the need for leaking - would help, but could never be more than a partial solution. Users would have to specify what they wanted to know. But where there is no reason to suspect something is amiss, no-one may bother to ask.

Another approach is to help potential whistleblowers pursue their concerns more effectively internally. A new charity, Public Concern at Work, provides legal and practical advice to concerned employees. It has already shown that it is able to help many employees raise concerns about misconduct within the organisation, sometimes having the problems remedied without publicity - or the victimisation that invariably follows.