Five hundred pages of files kept by the Polish police on Lech Walesa when he was leader of the striking Gdansk shipyard workers in the early 1980s have just gone up on the internet. Walesa . . . who went on to become president of Poland . . . put them there himself to confound those who have spread rumours that he was a police informer in the old days before Communism collapsed in Poland in 1989.

"I got sick and tired of the constant accusations, doubts and insinuations being peddled by these people and decided to publish these materials for all to see, " he said. It is the most dramatic move yet in an argument that has been raging in Poland for months, over whether all the old police files should be made public so that everyone who spied on colleagues or neighbours for the secret police can be identified.

What made Walesa such a controversial figure?

There were many brave men and women involved in the battle for civil rights in the old Communist states. One could mention the Russians Alexander Solzhenitsyn and Andrei Sakharov, the Czech Vaclav Havel, the Slovak Alexander Dubcek . . . all of them remarkable. But until 1989, no one defied Communist authority as successfully as Walesa.

In the summer of 1980, Communist Poland was paralysed by a strike of 100,000 workers protesting about increases in food prices. They elected a strike committee, with Walesa, an electrical engineer from the Lenin shipyard, as chairman, and created the Solidarnosc (Solidarity) movement, which the Communists never succeeded in suppressing. The situation was replete with irony.

Lenin, the founder of Communism, had exhorted workers to use the general strike as political. Now the self-professed Leninists who ruled Poland were forced to negotiate with a genuine strike leader who was not a Marxist but a practising Roman Catholic. In 1981, the crisis ended with a military coup.

What happened to Walesa after that?

Walesa spent seven years either under arrest or being harassed. In 1983, he was awarded the Nobel Peace Prize. In 1989, he was elected President of post-Communist Poland, but lost his position in the 1995 election. He stood again unsuccessfully in 2000, since when he has lectured around the world on the history and politics of central Europe. He is now 63.

Why should this story matter now?

All the old Communist regimes had extensive police networks which relied on information secretly passed on by informants, who spied on their neighbours or colleagues (the theme of the recent film The Lives of Others, which explored the police state that was the old East Germany).

There are an unknown number of exinformants still alive, perhaps still holding important jobs. In Poland, old police files are held by a trust called the Institute of National Remembrance. Every now and again, leaks emerge from historians with access to the archives. Last month, one of Poland's most eminent journalists, Ryszard Kapuscinski, who died in January aged 74, was "outed" as a former spy.

In March the Polish government brought in a new vetting law, which required 53 categories of professionals . . . including politicians, journalists, academics, head teachers and directors of publicly listed companies . . . to declare whether they had collaborated with the police. It applied to about 700,0000 Poles born before 1 August 1972, and to foreigners working in Poland.

Those who failed to sign a declaration before 15 May, or were caught lying, faced dismissal and other penalties. After widespread protests, the law was effectively annulled by the constitutional court. By that time, thousands had filled in their forms, but many others had refused, and were prepared to take the consequences.

What is wrong with exposing former informants?

There are Poles who personally have nothing to hide who vehemently oppose the sniffing out and naming of old collaborators, because of the mindset it induces. Too many people, they say, are obsessed with what happened before 1989, instead of dealing with the world they now live in.

Adam Michnik, a former Solidarity leader who now edits Poland's largest newspaper, has spoken of there being two Polands: "A Poland of suspicion, fear and revenge is fighting a Poland of hope, courage and dialogue." Lech Walesa was among those opposed to opening the archives, saying that it would destabilise Poland's democracy. But the counterargument is that while the information about ex-informants lies festering in the archives, it is a cause for suspicion, rumour and possibly even blackmail.

Exposure would clear the air.

Is this problem confined to Poland?

The same problem exists in every one of the countries that used to be under Communist rule, 10 of which are now members of the EU. In 1991, the Germans passed the Stasi Records Act, regulating access to the old East German police files. The law allows anyone who was spied on to see their file, and see who spied on them, but does not allow them to see the spies' files, to avoid the risk of revenge attacks.

This Stasi law is regarded as a model of its kind. It has been copied in most of the other former Communist states of Eastern Europe. After the fall of Saddam Hussein, the new Iraq government also sent observers to Germany to study the Stasi law before deciding what to do with the mountain of files assembled by the Ba'athist police.

This problem crops up wherever an oppressive regime has collapsed or been overthrown. In many cases wiser heads have argued that there is no point in exacting retribution. In France, after the war, the former prime minister Pierre Laval was shot, and the ex-president Marshal Petain died in prison, but a halt was called to further reprisals against Nazi collaborators. In Spain, after the death of Franco, the new democracy decided not to punish those who had worked with him, and most of the country has enjoyed political stability since. In South Africa, after the end of Apartheid, Nelson Mandela's government also chose reconciliation.