In the original script, the setting was 1957 and revealed that the Americans had launched a satellite in advance of the Russian Sputnik, only to have it knocked out of orbit by the Nostalgia Tours spacebus. Andrew Cartmel realised that the story was running overlength, it was decided to cut this element from the storyline, along with additional background on the Bannermen (revealing that they had polluted their own planet to the point that it was rendered uninhabitable).
A fairly well-known example within Doctor Who. Ray was almost the Doctor's newest travelling companion, but they decided to keep on Ace (from the next story) instead. Plus, Sophie Aldred auditioned for the role.
Nicholas Ball, Kenneth Colley, Michael Elphick, Michael Gothard, Bernard Hill, David Warner Jeremy Kemp, Ronald Lacey, T.P. McKenna, Clifford Rose, Simon Ward and Peter Vaughan were considered for Gavrok.