Question: Who was the author that penned the 6th installment of a trilogy that originated on BBC Radio 4 as a comedy broadcast in 1978?

Context articles: Colin MacDonald (writer)
The House of Milton Jones
And Another Thing... (novel)
Jeremy Mortimer
The Hitchhiker's Guide to the Galaxy
Tracy-Ann Oberman
I'm Sorry I Haven't a Clue
The Museum of Everything
The Penny Dreadfuls Present...
Neil Sleat

Colin MacDonald was born in 1956 in Inverness, Scotland.
 He is a prolific writer for television and radio.
 Television credits include "The Dunroamin Rising" (BBC1), "The Gift" (BBC1), "The Wreck On The Highway" (BBC1), "Sharpe's Honour" (ITV) and episodes in the series "Blue Murder" (ITV), "Heartbeat" (ITV), "Casualty" (BBC1), and "Para Handy" (BBC1).
 Radio credits include "Killing the Butterfly" (BBC Radio 4), "Hill of Rains" (BBC Radio 4), "The Colour of Summer" (BBC Radio 4), "King Of Hearts" (BBC Radio Scotland), "" (BBC Radio 4) and "Calum's Road" (BBC Radio 4).
The House of Milton Jones is a radio comedy series which was first broadcast in 2003 on BBC Radio 4.
 It was written by Milton Jones and James Carey, and starred Milton Jones as himself, Olivia Colman as Milton's sister Susan, Nigel Lindsay as Susan's husband Ian, Tom Goodman-Hill as Anton, and Rosemary Leach as Milton's Aunt Dilys.
 Re-runs are broadcast on BBC Radio 4 Extra (formerly known as "BBC 7" and "BBC Radio 7").
And Another Thing... is the sixth installment of Douglas Adams' "The Hitchhiker's Guide to the Galaxy" "trilogy".
 The book, written by Eoin Colfer, author of the "Artemis Fowl" series, was published on the thirtieth anniversary of the first book, 12 October 2009, in hardback.
 It was published by Penguin Books in the UK and by Hyperion Books in the US.
 Colfer was given permission to write the book by Adams' widow Jane Belson.
Jeremy Mortimer is a British director and producer of radio dramas for BBC Radio.
 He is the son of John and Penelope Mortimer and the half-brother of Emily Mortimer.
 His credits include "The Pattern of Painful Adventures" (BBC Radio 3, 2008) and radio adaptations of "Daphnis and Chloe" (BBC Radio 4, 2006), "Philomel Cottage" (Radio 4, 2002) and "The Time Machine" (Radio 3, 2009).
 His production of the Troy Trilogy, which featured Paul Scofield and was first broadcast on Radio 3 in 1998, was lauded as "the greatest radio drama [anyone] could ever hear."
The Hitchhiker's Guide to the Galaxy (sometimes referred to as HG2G, HHGTTG or H2G2) is a comedy science fiction series created by Douglas Adams.
 Originally a radio comedy broadcast on BBC Radio 4 in 1978, it was later adapted to other formats, including stage shows, novels, comic books, a 1981 TV series, a 1984 computer game, and 2005 feature film.
 A prominent series in British popular culture, "The Hitchhiker's Guide to the Galaxy" has become an international multi-media phenomenon; the novels are the most widely distributed, having been translated into more than 30 languages by 2005.
Tracy-Ann Oberman (born Tracy Anne Oberman, 25 August 1966, Brent, Greater London) is an English television, theatre and radio actress.
 Best known for her role as Chrissie Watts in BBC1 soap opera "EastEnders" from 2004–05.
 Also a writer, Oberman has contributed to a number of radio sketch shows and in 2008 co-authored with Diane Samuels the play "Three Sisters on Hope Street".
 In 2010 she wrote and starred alongside Catherine Tate in her BBC Radio 4 play "Bette and Joan and Baby Jane" and in 2012 wrote the BBC Radio 4 play "Rock and Doris and Elizabeth".
 In 2015 she wrote and starred in the third part of her Hollywood Trilogy for BBC Radio 4, "Mrs Robinson, I Presume", alongside John Simm and Kevin Bishop.
 Oberman was a regular columnist for "The Guardian" newspaper during 2007.
I'm Sorry I Haven't a Clue is a BBC radio comedy panel game.
 Introduced as "the antidote to panel games", it consists of two teams of two comedians "given silly things to do" by a chairman.
 The show launched in April 1972 as a parody of radio and TV panel games, and has been broadcast since on BBC Radio 4 and the BBC World Service, with repeats aired on BBC Radio 4 Extra.
 The 50th series was broadcast in November and December 2007.
The Museum of Everything is a BBC Radio 4 comedy sketch show, written and performed by Marcus Brigstocke, Danny Robins and Dan Tetsell with Lucy Montgomery.
 The show generally occupied the 18:30 comedy slot on BBC Radio 4, with repeats several times a year on BBC Radio 4 Extra.
 The first series was broadcast in 2004, a second series in 2005 and a third series in summer 2006, the latter of which made continued use of favourite characters from past episodes as well as creating new ones.
 It is set in the fabled "Museum of Everything", an apparently infinite space housing exhibitions on everything from the history of stairs to the Greek buttock gallery.
The Penny Dreadfuls Present... is a British radio comedy programme, written and performed by comedy troupe the Penny Dreadfuls, with each episode looking at a different member of The Brothers Faversham, a collection of heroes of Victorian Britain.
 The first series was produced and broadcast by the BBC for BBC Radio 7 and aired between January and February 2008.
 The second series was broadcast in October 2008, and was repeated on BBC Radio 4 in December 2008 and January 2009.
 An episode on Guy Fawkes was broadcast in BBC Radio 4's "Afternoon Play" slot on 5 November 2009.
Neil Sleat is a newsreader and continuity announcer on BBC Radio 4.
 After joining the BBC as a trainee engineer, working as a studio manager and then an announcer/newsreader on the BBC World Service, he joined Radio 4 as an announcer/newsreader in 1998.
 He has also produced many BBC Radio 4 trails.
 He returned to BBC Radio 4 in May 2006 after several months away producing trails full-time.