I remember attending a lecture given by Geza Vermes in Oxford a year or so after the broadcast, probably in early 1986. He talked about his own experiences in filming the documentary and the backlash against it among Christians in the media. I recall, in particular, his smiling at the repeated complaint about its one-sidedness, with only one minute given to I. Howard Marshall.
Update: Many thanks to Geza Vermes for emailing with the information that the library is Dr Williams' Library in London. The lecture I remembered is "Jesus, the Evidence and the British Press" and it is included in a collection of papers to appear on 4 January 2010 in SEARCHING FOR THE REAL JESUS published by SCM Press.