Prosecutors say they will seek to establish whether Lech Walesa's handwriting matches the signatures of a purported communist-era agent, as they investigate collaboration allegations against Poland's former president.

Walesa, the 1980 Solidarity freedom movement founder, on Wednesday met with a prosecutor of the National Remembrance Institute in Warsaw, who questioned him about recently revealed documents that suggest Walesa was an informant for the communists in the 1970s, codenamed Bolek. Walesa rejects the allegations.

The institute's communique said Walesa was shown the files and denied their authenticity. Some of the documents bear "Lech Walesa" or "Bolek" signatures.

The prosecutors will now seek an opinion from handwriting experts who will compare various Walesa signatures with those on the documents.

Solidarity peacefully ousted communists and paved the way for Poland's democracy.