Complex sentence: At the same time a possible drama on the Stalker affair was being considered by Zenith Productions, a production company involved with a number of British cinema films in the mid 1980s and also the "Inspector Morse" series for television.
Split into simpler sentences: At the same time Zenith Productions were also considering a possible drama on the Stalker affair. Zenith was a production company that had been involved with a number of British cinema films in the mid 1980s, and was also making the "Inspector Morse" series for television.