Duff says: "Bronislaw Geremek, who escaped a child from the Warsaw ghetto, was the man who brokered the deal in the late 1980s between the communist government and the Solidarity movement. The collapse of the totalitarian regime in Poland led to the eventual end of the Soviet system and the reunification of Europe.
"In Bronislaw's tragic death, Europe has lost one of its heroes. It was a wonderful privilege to work closely with such a man."
Mr Geremek died in a car crash on 13 July.