Former Polish president and Solidarity founder Lech Walesa was a paid informant for the Communist-era secret security service between 1970 and 1976, recently seized documents allege.
Mr Walesa has admitted signing a commitment to be an informant but has insisted he never acted upon it. He was cleared by a special court in 2000.
Lukasz Kaminski, head of Poland’s National Remembrance Institute, said documents seized from the house of the last Communist interior minister, the late General Czeslaw Kiszczak, include a commitment to provide information to the secret security signed in Mr Walesa’s name and a codename, Bolek.
There are also pages of reports and receipts for money apparently signed by Mr Walesa.
The 279 pages of documents will be made public in due course, Mr Kaminski added. He said historians needed time to analyse the content of the documents.
Mr Walesa, 72, speaking from Venezuela, where he is travelling, said the papers were fake.
“There can exist no documents coming from me. I will prove that in court,” he said. Communism and Moscow’s control were imposed on Poland and other eastern European countries after the Second World War.
Secret security was the regime’s harsh tool for keeping the people under control, using personal information to blackmail and discredit critics. Mr Walesa was the icon of Poland’s and eastern Europe’s drive for freedom which brought down the Iron Curtain in 1989 without bloodshed.
He founded and led the Solidarity trade union from 1980, and was Poland’s president from 1990 to 1995.