Production block

A production block is a device used by the production manager — in consultation with the producers, executive producers and senior department heads — divides the principal photography schedule so as to more efficiently maximize the talents of both behind-the-scenes personnel and actors. Instead of filming and contracting for single episodes, people such as directors, line producers, directors of photography and some actors — along with many other individuals — are assigned to groups of episodes, which may later be broadcast in a completely different order. Reasons for combining certain episodes into production blocks include: availability of talent, the need to use the same locations in multiple episodes, the necessity of certain episodes to have the same sort of background weather, or a perceived ability to save money by filming certain episodes together. Production blocks always vary by the needs of a particular series, and can overlap, as happens intentionally on the BBC Wales version of Doctor Who through double banking.

History
Production blocks are a staple feature of the BBC Wales version of Doctor Who and her sister shows. An obvious sign of the use of production block is the fact that at least a few episodes each series have been broadcast in a different order than that in which they were produced. Generally, a production block consists of two episodes, but they have been as few as one (as in the case of "Doctor-lite" and most "special" episodes) or as many as four (as with Rise of the Cybermen/The Age of Steel/Army of Ghosts/Doomsday). Production blocks are assigned simple ordinal numbers, thus allowing clappers to identify filmed scenes not by name, but a numerical code, which somewhat assists with keeping the identity of various filmed scenes private from the public. The BBC Wales calendar sometimes — but not always — allows for production to take a short break between production blocks.

However, it should not be assumed that production blocks are an innovation of BBC Wales and thus "modern" television production. Doctor Who has always been divided into production blocks. Although the first serial to be broadcast out of order was The Curse of Peladon, production blocks were used by the BBC at Television Center and its predecessors to derive an overall budget for a season. Thus, in the 1960s, the meaning was slightly different than was later used. A "production block" was, roughly, an entire season's worth of episodes. However, because seasons were very much longer in the 1960s, one serial from the outgoing production block was held over to start the new broadcast season. This allowed the production team a "cushion" against unforeseen disasters. For example, Galaxy 4 was technically a part of the second production block, but broadcast as the opener to season 3. In early Doctor Who history, the equivalent to the BBC Wales "production block" was called a "recording block". This was generally around 6-8 episodes in length and tended to be staffed by the same people. A few good examples of a recording block are The Rescue/The Romans and The Time Meddler/Galaxy 4/Mission to the Unknown. Recording blocks were the basic division of the schedule in which most production personnel operated. Designers were often assigned to entire blocks, as with Raymond Cusick for The Rescue and The Romans. Actors' contracts were often conceived in terms of full or half recording blocks. These blocks or half blocks then usually corresponded to whole serials — but not always. Due to restructuring of stories after contracts were signed, for instance, Jackie Lane, Michael Craze and Anneke Wills were all written out mid-serial.

the demarcation between production blocks was perhaps most easily recognized by the deisgners, who were often assigned by block rather than serial. For instance, The Rescue and The Romans were a single production block, designed by Raymond Cusick''