Cast as Miller in Force 10 from Navarone (1978) but left the production because of a clash with the producer, and was replaced by Edward Fox.
Cast in in The Island of Dr. Moreau (1977) but was replaced by Nigel Davenport.
Considered giving up acting to become a monk.
Director John Schlesinger cast him as a replacement for Alan Bates in the part of well-off homosexual doctor Daniel Hirsh in his controversial film Sunday Bloody Sunday (1971), after Bates was deemed unavailable to shoot. According to screenwriter Penelope Gilliatt, Bannen never felt comfortable with the part; she speculated that he was flustered by the fact that he would have to kiss male actor Murray Head, who played his lover whom also carried on an affair with Glenda Jackson. The anxiety adversely affected his performance during the early filming. Schlesinger had to fire him and replace him with Peter Finch, who won an Oscar nomination for the role. Many observers believe that Finch lost the Oscar to Gene Hackman because of the gay kiss. Bannen said near the end of his life, after being hailed for his comeback in Waking Ned Devine (1998), that this was his one big regret, for throwing away the plum role seriously set back his career and it never recovered.
He died in a car accident in 1999 while a passenger in a car driven by his wife, Marilyn. Coincidentally, Bannen originally met his wife back in 1976 when she parked her old van in his reserved parking space and was unable to get it started.
He was awarded the 1981 London Critics Circle Awards (Drama Theatre Awards) for Best Supporting Actor of 1980 for his performance in "Translations".