Poland's ruling conservatives, led by Jaroslaw Kaczynski, have leapt at the opportunity to question Walesa's independence from the communist-era police after he became Poland's first democratically elected president between 1990 and 1995.

His defenders say that whatever the authenticity of the documents, they do little to undermine the record of a man who was awarded the Nobel Peace Prize in 1983.

Walesa, 72, has said a batch of files found last week at the house of a late communist interior minister was fabricated, and denied he ever spied on fellow dissidents, an accusation he has faced repeatedly over two decades.

The new files contain a handwritten document signed "Lech Walesa" which includes a pledge to cooperate with the secret service. It mentions the codename "Bolek", long ascribed by critics to Walesa.

Other documents include typed descriptions of conversations with Bolek in which he describes the mood among workers in the Gdansk shipyard where Walesa was working at the time and where the Solidarity movement originated. There are invoices, apparently signed by "Bolek" for cash received in return for information.

Scans of the files have been published in the Polish press. Some of the documents appear to have been written by secret police officials and some by Walesa.

Poland's Institute of National Remembrance (IPN), a state agency tasked with investigating crimes "against the Polish Nation" from World War Two until the collapse of communism, has said the documents in its possession are authentic, meaning they did originate from the secret service.

Forensic testing of the documents, including of handwriting purported to be Walesa's, is under way. 

LEGEND

Walesa's critics argue the files put into question not only Walesa's standing as a hero of the effort to end communist rule but also raise doubts about whether the country ever succeeded in fully shaking off the influence of pre-1989 communist officials.

"The (Walesa) legend probably cannot be defended any more," Foreign Minister Witold Waszczykowski told public television.

"We need to ask historians whether these issues linked to Lech Walesa and maybe others ... may have served as obstacles in the 1990s in terms of taking important decisions about state security."

Antoni Macierewicz, defence minister, went further, saying the files proved that post-communist Poland was a product of the secret police and not of democratically-elected institutions.

"The legend of Lech Walesa is ending. He will disappear into the past just as he deserves," Macierewicz said. "This issue shows the real truth behind (post-communist Poland)."

"It shows that (secret police) files were being used to blackmail people. An entire group of people had become a tool in the hands of the communist regime which used them to obtain power and influence," he said.

Liberal politicians and commentators in turn accused officials of the ruling Law and Justice (PiS) party of blackening Walesa's image and Poland's democratic achievements for political gain.

Critics say the party is using nationalist language to delegitimise previous governments and bolster its support, mindful that it will be difficult to make good on its promise of substantial financial help for poorer voters.

PiS swept into power in October last year, after nearly 10 years in opposition, on a pledge of more economic equality at a time when many voters feel left behind despite Poland's overall economic success.

"Walesa is an opportunity for PiS to cover up economic issues," said Tadeusz Bartos, a humanities professor and liberal commentator.

"The party wants to have its vision recognised," he said. "It's a vision that says Poland has suffered since (the collapse of communism), it lacked independence."

BOLEK AND THE TWINS

Hostility between Walesa and Kaczynski, and to his late twin President Lech Kaczynski, dates back to the early 1990s.

Walesa was Poland's first fully democratically elected president after World War Two at the time, and the brothers were close aides. But they fell out over Walesa's refusal to abandon painful free-market reforms during his five-year term.

The twins' political allies have since blamed economic policies in the early 1990s for the hardships experienced by many Poles when communist-era industries were being closed down or privatised.

The conflict has intensified since the October election. Walesa accuses Kaczynski - who is not in government but is widely seen as the behind-the-scenes decision-maker - of undermining democratic institutions, a concern echoed by some European Union officials.

The twins repeatedly accused Walesa of collaboration but a special court exonerated the former president in 2000.

The IPN said handwriting experts and others had not yet ascertained whether Walesa had in fact signed the newly-discovered documents or whether they were falsified, as the former dissident claims.

The forensic investigation could take a long time. But some of Walesa's former fellow-dissidents have argued its findings will be irrelevant.

Even if his resolve wavered during a wave of repression in the 1970s, when police killed dozens of protesters during anti-government strikes, his subsequent role in fighting communism was undeniable, they said.

"If anyone tells me that Lech should apologise for something then I would say: Maybe you should apologise to Lech Walesa for not standing behind him then," Wladyslaw Frasyniuk, once a Solidarity activist, told Gazeta Wyborcza daily.

The debate over Walesa's past revives the dilemma faced by all former Soviet satellite states on how to balance the need for truth to be exposed with the risk that secret files may have been doctored or falsified by communist-era officials.