It has become common to insist that the commission has no useful purpose. Two reasons are usually cited. The first insists that public resources are being wasted on an African National Congress (ANC) quarrel. The second suggests that, since the commission is unlikely to be able to give a watertight finding, it is a waste of effort. Both miss some important points.

First , this is not simply an internal ANC dispute: the credibility of key public office-bearers is at stake. An apartheid-era spy is a devious person who may have delivered people up to unaccountable state power. If a spy heads a national prosecuting authority, that person may be compromised in how he or she discharges his or her office. So the allegations against Bulelani Ngcuka reflect on his character and on whether he is able to act fairly in his post. These are matters of public concern which should be investigated. Since spying for the apartheid authorities is not a crime, a commission seems the appropriate vehicle.

Ironically, those who complain about public resources being used to test the spying claims seem unaware of the message which would have been sent if this dispute had been left to the ANC that the fitness for office of the national director of prosecutions is a matter for the governing party alone. Appointing a commission confirms that this issue affects all and should be investigated by an inquiry accountable to the whole country.

But what about the argument that the commission cannot produce a definitive finding and so is a waste?

The importance of its role does not rest on whether it can produce a watertight verdict. While allegations that a public official was an apartheid-era police spy are matters of public interest, there are great dangers if we do not impose on those who make the claims a burden to provide convincing evidence. Accusing someone of spying is an easy way to destroy a career, as it is impossible to prove one was not a spy the mud may stick, even if it is not backed by evidence.

Already, the commission's appointment has forced Ngcuka's accusers to produce evidence and, so far, they have failed. If that continues, the commission can play a vital role if it points out that the onus of proving spy charges rests with the accusers and that, if they fail to meet the test, it is they rather than whomever they accuse who face a credibility problem.

If all the commission does is to establish the principle that people who make spying allegations must substantiate them or be disbelieved, it will have made an important contribution to building democracy. More is at stake than whether particular office holders have been fairly accused. The allegations against Ngcuka are only part of a saga in which we have seen the re-emergence of the clandestine politics of the apartheid era in which accusations of spying or dishonesty were used as weapons in political battles.

That style of politics may have low costs during a fight against tyranny. But it is deeply damaging to democracy: when no one knows whether allegations against public officials are based on evidence or a desire for position, the credibility of our representatives and institutions is in serious trouble. The result may be pervasive public cynicism: many may conclude that democracy is pointless because it is a vehicle for smear politics rather than public service. It is important, therefore, that this trend towards clandestine politics be curbed.

The way to do this is not, as some have argued, by insisting that political leadership prevent allegations being aired. The only antidote to clandestine politics is open politics the cure is not to hush up the claims but to ensure that those who make them must back them in public with strong evidence if they want to avoid ridicule.

Testing these claims in a commission can signal that the politics of the back alley will not work here, because the pressures to force it into the open and to subject it to public scrutiny are too strong to allow smears to remain untested.

Insisting that a commission is only of use if it can come up with a finding which will immediately end a dispute is short-sighted. Often, the fate of societies battling to become democratic is not settled by quick fixes but by building precedents for the longer term. If the commission establishes that the politics of smear can be dangerous for those who engage in it without evidence, it may help our political future far more than an immediate "remedy" with a limited effect on the way we conduct our politics.

Friedman is senior research fellow at the Centre for Policy Studies.

With acknowledgements to Friedman and the Business Day.