Recently seized documents show that Poland's former president and Solidarity founder Lech Walesa was a paid informant for the communist-era secret security service, the head of the country's history institute has said.
Mr Walesa, the 1983 Nobel Peace Prize laureate, has previously acknowledged signing a commitment to be an informant but has insisted he never acted on it.
In 2000, he was cleared by a special court which said it found no evidence of collaboration.
Lukasz Kaminski, head of the National Remembrance Institute, said documents seized from the home of the last communist interior minister, the late General Czeslaw Kiszczak, include a commitment to provide information that is signed with Mr Walesa's name and codename, Bolek.
There are also pages of reports and receipts for money in the 1970s, signed Bolek.
Mr Walesa (72) in a written message from Venezuela where he is travelling, suggested the papers are fake.
“There can exist no documents coming from me. I will prove that in court,” he said.
The 279 pages of documents will be made public in due course, Mr Kaminski said. He added that historians need time to analyse their content.
Antoni Dudek, the institute's leading historian, said the impact would not be that great unless some evidence emerged Mr Walesa continued to be an informant after he had founded the Solidarity freedom movement.
“Lech Walesa is the symbol of Poland’s struggle for freedom, he is the symbol of Solidarity and nothing can destroy that, unless we learn that he continued that collaboration,” Mr Dudek said.
According to Mr Kaminski, five more packets of seized documents have not yet been opened. Prosecutors and police were also searching Mr Kiszczak’s summer house.
Communism and Moscow's control were imposed on Poland and other countries in the region after the Second World War and were despised and opposed by most people.
Secret security was the regime’s harsh tool for keeping the people under control, using personal information to blackmail and discredit opponents and dissidents.
The papers concerning Mr Walesa came to light when Mr Kiszczak’s widow offered to sell the institute documents concerning secret informer Bolek.
Prosecutors seized the documents the same day because the law requires important historic papers to be handed in.
Mr Walesa was the icon of Poland and eastern Europe’s drive for freedom that abolished communism and brought down the Iron Curtain in 1989 without bloodshed.
He founded and led Solidarity from 1980 when it was formed out of worker protests, and through communist-imposed martial law.
He led Solidarity in round-table negotiations with the communists in 1989 that ushered in democratic and economic change.
He was Poland's first popularly-elected president from 1990 to 1995 but following a term of office where his style was perceived as authoritarian, he painfully lost a re-election bid to ex-communist Aleksander Kwasniewski.