Production unit manager was a new post created at this time. The functions of this post - basically financial planning - had previously been carried out by the producer.
Season eleven was planned during a period when producer Barry Letts and script editor Terrance Dicks were dividing their time between Doctor Who and Moonbase 3, a new six part space adventure series that they had created and been asked to make for the BBC. Moonbase 3's studio recordings were scheduled to be carried out in the break between Doctor Who's tenth and eleventh production blocks so that there would be no direct clash of commitments, but the two men nevertheless had their work cut out to ensure that neither series suffered through lack of attention.
Adding further to their workload was the need to devise and cast a new companion for the Doctor following the departure of Katy Manning's Jo Grant at the end of The Green Death. The character they eventually came up with, after a false start involving an unknown character played by an unknown actress, was journalist Sarah Jane Smith, and the actress Letts chose, with Jon Pertwee's approval, was Elisabeth Sladen. Sladen made her debut in the season's opening story, The Time Warrior - which, like Carnival of Monsters the previous year, was made not at the beginning of the new production block but at the end of the old one.
The eleventh season, while certainly having some high points, is arguably the weakest of Jon Pertwee's time as the Doctor. The impression given is that, with the notable exception of newcomer Elisabeth Sladen, the series' regulars - both in front of and behind the cameras - were running short of energy, ideas and enthusiasm.
The departure of Pertwee, following on from the death of Roger Delgado and the bowing out of Katy Manning and Richard Franklin, marked the end of an era in more ways than one. Regeneration was in store, however, not only for the Doctor but also for the production team.
Planet of the Spiders was Terrance Dicks's last story as script editor and Barry Letts's penultimate one as producer; although Letts would stay on to oversee the early part of season twelve, it would be his successor Philip Hinchcliffe, along with new script editor Robert Holmes, who would be responsible for steering Doctor Who into the next phase of its history.