By Anna Koper
WARSAW (Reuters) - Poland's government-affiliated history institute said on Tuesday it had new evidence that Lech Walesa, who led protests and strikes that shook communist rule in the 1980s, had been a paid informant for the secret police in the 1970s.
A lawyer for Walesa, whose leadership of the Solidarity trade union contributed to the fall of communism throughout eastern Europe, said the evidence could be faulty and asked to question the assessors.
The Institute of National Remembrance (IPN) said a handwriting study had proved the authenticity of documents suggesting that Walesa, who was awarded the Nobel Peace prize and became Polish president, had collaborated with communist rulers.
It said he had provided at least 29 reports signed "Bolek", a codename long ascribed to Walesa, but did not say what they contained.
"There is no doubt," investigator Andrzej Pozorski told a news conference. "A handwritten agreement to collaborate with the Security Police from Dec. 21, 1970, was written in its entirety by Lech Walesa."
Pictures of the moustachioed former electrician being borne aloft by workers occupying the Gdansk shipyards became an inspiration for anti-communist movements across the Soviet bloc.
Walesa, now 73, has acknowledged once signing a commitment to inform, but he insists he never fulfilled it, and a special court exonerated him in 2000.
The issue has flared up again since the conservative, nationalist Law and Justice (PiS) party of Jaroslaw Kaczynski, also a former anti-communist activist who fell out with Walesa in the 1990s, won power in 2015.
The PiS argues that Poland lost sight of its Catholic national identity and of social justice in the transition to democracy and eventual membership of the European Union.
Any suggestion that Poland remained under communist influence despite ending totalitarian rule in 1989 - notably that Walesa might have been controlled by former secret police as president in 1990-95 - strengthens the PiS narrative.
"We don't want to remove Walesa from history books," IPN head Jaroslaw Szarek told reporters. "What changes is how he can be evaluated."
"Starting today, we can ask a new question: ... to what extent Lech Walesa's collaboration in the early 1970s determined his subsequent decisions ... in the 1980s and after 1989. This question remains open."
Pozorski said the IPN, set up in 1998 to investigate crimes "against the Polish nation", had reviewed 17 cash receipts and concluded they were written by Walesa.
Walesa's legal representative, Jan Widacki, said the examination did not amount to scientific evidence and asked to question the assessors.
"Walesa's handwriting today is not Walesa's handwriting from the '70s when he was a simple laborer," he told the public television channel TVP Info.
The documents surfaced last year at the house of a late communist interior minister.
The PiS campaigned in 2015 on a promise to help the poor, accusing past rulers of abandoning a vast number of working Poles when they instituted painful free-market reforms.
Walesa's defenders say that, whatever the authenticity of the documents, they cannot undermine his merits in leading efforts to shake off communist rule.
"His is a legend of a man who isn't born a leader but becomes one," historian Jan Skorzynski told the liberal daily Gazeta Wyborcza. "A man who, despite his weakness, could rise again and lead a movement. Perhaps his experience in the 1970s made him into such an effective leader during the 1980 strike."
Throughout post-Soviet Europe, historians have warned that communist-era secret police files are hard to interpret, because documents were sometimes falsified and witnesses coerced.
Historians have said Poland's communist government tried to dissuade the Nobel committee from awarding the Peace Prize to Walesa by offering falsified documents that he had collaborated when he led Solidarity between 1978 and 1981.
(Additional reporting by Marcin Goettig; Writing by Lidia Kelly and Justyna Pawlak; editing by Ralph Boulton)