The whole series is a spoof/hoax
No books exist that are written by Garth Marenghi because he is a fictional
character, you can read up on this at http://en.wikipedia.org/wiki/Garth_Marenghi
I know I was disapointed because I love the show and if he was a legit author I probably would have bought a book. Also the show was not filmed in the seventies/80's but was filmed using the production values of those times, ex. no amazing special effects, etc. You can read more on this at
http://myweb.tiscali.co.uk/thegoalra...place/faq.html
Who knows as the popularity grows someone might write a book under his name. lol
