The part of Neal Mottram was written as British but an American performer was chosen to play him.
Among those considered for the role of the Solicitor were Joss Ackland, Harry Andrews, Robert Flemyng, Peter Cushing, Michael Hordern, Kenneth More, Richard Todd, Nigel Stock, Patrick Troughton, Donald Houston, Frank Finlay, Freddie Jones, and Dennis Price.
Considred for the major role of Wall was Tom Adams.