1979 had seen the end of the turbulent Graham Williams era of the show. It had been highly criticized for a lack of substance and too much comedy, but Williams had had a number of behind-the-scenes problems to deal with. In late 1979, John Nathan-Turner took over the role of producer having worked for two years as a production unit manager. 'JNT', as he became known, wanted to stamp his authority on the show and get it back on an even keel. Initially he was reluctant to use writers and directors that had worked on the show previously hoping that fresh blood would inject new life into the proceedings.
The 18th season of Doctor Who, and Tom Baker's last, certainly felt new. Not only had the opening titles been changed for the first time in seven years, but also a new contemporary theme music was introduced and there was a new costume for the Fourth Doctor. The look of the show was vastly changed with JNT making sure that large parts of the budget was spent on the onscreen areas. They were changes that not everyone had liked.
One of JNT's early jobs was to cast a new actor in the role of The Doctor, and he was aware that anyone following Tom Baker would need to be vastly different. A youthful Peter Davison was eventually cast, who was well known for roles in All Creatures Great and Small and Sink or Swim. The public in general liked what they saw of this new Doctor, and viewing figures increased.
Aware that the 20th anniversary of the show was approaching, JNT made early plans for a celebratory episode not unlike The Three Doctors. His vision was for all surviving actors who had played The Doctor to be reunited. JNT and script editor Eric Saward first began planning in August 1981 and contact was made with David Reid (head of serials) who was happy for such a story to take place. However due to Peter Davison's role in the popular comedy Sink or Swim the production of the entire series of Doctor Who had to shift, meaning no season was set to be broadcast in the actual anniversary. As a result, the commemorative adventure would become a one-off isolated episode.
In the November of 1981 Peter Davison's first full season was fast approaching. The public were to get an early viewing of the new Doctor in costume at The Lord Mayor's Parade in London on the 14th of that month. This annual event had been running since 1535 and Doctor Who, and the Daleks in particular, had been the stars before in 1972. Three Daleks (including a gold coloured fan built prop) starred with Davison on the BBC float, including, reunited for the first time since the 1960s, the shoulders and skirt of Dalek Seven. Also appearing on the float was Dalek One-ii. Both BBC props had been seen a small amount of refurbishment having been repainted and generally tidied up.
Meanwhile work continued on the Anniversary special and although JNT was reluctant to use previous writers, Saward convinced JNT to look over the work of Robert Holmes who had been one of the most well-received writers on the show. JNT was persuaded to ask Holmes if he would like the job of scripting the anniversary episode, although Holmes was reluctant as he didn't like to use other writers' creations. Eventually he agreed and set about producing some possible storylines in august 1982. These didn't include the Daleks.
Holmes was never comfortable with writing for unfamiliar characters, and he expressed concerns that he was struggling with the remit. Saward duly contacted another long term contributor to Doctor Who, Terrance Dicks, to ask if he would be on standby. October saw Holmes formally give up on the project and Dicks quickly stepped in with ideas of his own. Dicks insisted the Daleks had to be part of an anniversary celebration, and his storyline was commissioned soon after on 16th November.
In the meantime JNT was searching out a director to deal with the complexity of the work involved and ultimately Peter Moffat was selected due to his work on the previous stories State of Decay, The Visitation and Mawdryn Undead.
The script development still had problems due to the constant flux of actors availability. Cameo parts which had been written in had to be removed and others invented as other actors became available. Once it had been decided to include the Daleks in the episode, it was suggested quickly that they remain in studio due to the problems of filming on location. The Cybermen and Master would be employed as the main enemies and as such it turned out just one Dalek would be needed for the short cameo.