I discovered this film while I was reading some history of Leon Trotsky, when I got to the popular culture section I noticed the name of the film there, and the fact that it stars Richard Burton which raised an eyebrow for me. And it's not the first time that I've seen Burton playing as a notable communist figure, first being in Sutjeska (1973) as Josip Broz Tito.
The film itself is listed in the book "The Fifty Worst Films…