- You may be looking for David Agnew.
The BBC in the late 1970s took a dim view of producers and script editors commissioning themselves, and thus putting a writer out of a job, so when the occasion did arise, then-Doctor Who producer Williams disguised his actual authorship. 2|entertain did a tongue-in-cheek feature on The Invasion of Time DVD called "The Elusive David Agnew". The featurette included Terrance Dicks stating that Agnew was a good friend of Robin Bland (the pseudonym Robert Holmes credited Dicks under on The Brain of Morbius). As a final joke, the director credit on the featurette is given to Alan Smithee, an infamous pseudonym used for decades by Hollywood film and TV directors, usually those who feel too disappointed at the outcome of their work to risk putting their names on it.
Contrary to the mystery perpetuated in the comedy featurette The Elusive David Agnew, the identity of "Agnew" to Doctor Who is known.
- Anthony Read, (the script editor, at that time) collaborated with Graham Williams on the scripts for The Invasion of Time, written at the last minute to replace Killers of the Dark by David Weir which would have proven too expensive to shoot even on a film budget.
- Douglas Adams (the then-current script editor) and Graham Williams on City of Death as a late replacement for David Fisher's A Gamble With Time.
Coincidentally, on both occasions the pseudonym was used, it was for scripts whose original writers had the first name 'David'.