His tenure as script editor, covering the latter part of Season 5 (starting with "The Web of Fear") and the start of Season 6, was a turbulent time for Doctor Who, in which scripts in developtment were repeatedly deemed unworkable and abandoned, requiring frequent last-minute commissioning of new scripts and bringing forward scripts scheduled for later in the season.
Sherwin's sole writing credit on Doctor Who was "The Invasion", an eight-part epic Cyberman story. He also wrote, uncredited, the first episode of "The Mind Robber" that had been added onto the start of the story due to the preceding story being shortened by an episode, and had to use only the three regular actors, the TARDIS set, a blank studio and some spare BBC props.
He was credited as producer on only two stories, but they were two of the most important in Doctor Who history, Second Doctor Patrick Troughton's last story (and the last black-and-white story) "The War Games", which introduced the Time Lords to the show, and Jon Pertwee's first story (and the first colour story) "Spearhead from Space", which introduced the new format of the Doctor being stranded on Earth in exile and forced to work for the United Nations Intelligence Taskforce (UNIT) as their scientific advisor. Sherwin took credit for both these innovations.
