Wałęsa, an ex-president and the former leader of the Solidarity trade union which helped bring down communism in Poland, has previously slammed such claims as “lies”.
But the state-run Institute of National Remembrance on Tuesday presented an analysis by graphology experts which concluded that documents signed in the 1970s by an informer codenamed “Bolek” were in handwriting the same as that of Wałęsa.
Files found in the house of communist-era Interior Minister general Czesław Kiszczak following his death in late 2015 allegedly contained a personal file and a work file of a secret collaborator.
The documents, from a time before the Solidarity union was formed, included a handwritten note signed "Lech Wałęsa - Bolek" in which the signatory vowed to collaborate with communist security services.
Files dating from between 1971 and 1974 indicated Wałęsa had received PLN 11,700 for 41 reports informing on some 40 workers at the Gdańsk Shipyard, broadcaster TVP reported.
Wałęsa has previously admitted that he had “made a mistake”, but denied that he was ever a paid secret agent who collaborated with the communist regime. On Sunday he claimed that documents found in Kiszczak’s house were forgeries.
According to earlier publications by several historians, Wałęsa broke off cooperation with the communist secret services several years before the landmark 1980 strike in the Gdańsk Shipyard, a protest that led to the birth of the Solidarity trade union and Wałęsa's meteoric rise to international fame.
Between 1990 and 1995, Wałęsa served as Polish president. He won the Nobel Peace Prize in 1983.
'We do not intend to remove Lech Wałęsa from Polish history'
The president of the IPN, Jarosław Szarek, told a press conference on Tuesday: "We do not intend to remove Lech Wałęsa from Polish history.” But he added: “The way Lech Wałęsa is seen is changing.”
Szarek told reporters: “From today there are no doubts about Lech Wałęsa’s collaboration with the [communist] security services.
“However, from today a new question can be asked (...) to what extent did the fact that Lech Wałęsa started this collaboration in the early 70s determine his decisions at a later date, in the first 16 months of Solidarity, later in the 80s, and also after 1989” following the collapse of communism in Poland.
“This is an open question," Szarek added.