Ronnie Marsh

 was head of serials (variously called "head of drama series" and "head of drama serials") at the British Broadcasting Corporation for a significant portion of the 1970s. He was particularly associated with oversight of the Jon Pertwee era. In 1970, he and Barry Letts conspired to move the series away from the cost-saving of experiment of season 7's seven-parters and return to shorter stories. Thus he and Letts put a ban on any serial longer than six parts so as to offer more first episodes and, hopefully, even higher ratings. This policy held for the remainder of the run of Doctor Who, save for the uniquely-constructed "four-part fourteen-parter" of Trial of a Time Lord. As head of serials, he could affect individual lives enormously. For instance, in 1970 he gave the career of director Michael Briant a boost by offering him a year's contract of freelance directing assignments,, which undoubtedly brought him before Barry Letts' eyes. Briant would go on to direct four serials for Doctor Who off the back of his Marsh-contracted 1970 BBC projects.

Robert Holmes remembered his stewardship of the Pertwee era for its cognizance of the power of Mary Whitehouse's organisation. Indeed, others confirmed that Marsh tended to intervene in production when he thought the show was getting close to "dangerous ground". For instance, he made the costly step of reversing a casting decision on Colony in Space, because he thought having Susan Jameson in the role of Morgan might have sexual overtones. (REF: The Third Doctor Handbook)  He likewise was keen to ensure that The Master not be seen "raising Azal, the Dæmon, inside the village church, as it would offend too many people".

In the latter half of the 1970s, it was he that commissioned and strongly supported Blake's 7. However, this led to an edict that banned writers from contributing to both Doctor Who and Blake's. This had the effect of stopping at least one Chris Boucher Doctor Who script from seeing completion. (Doctor Who Magazine #197)