It is being sold at Phillips Bayswater on 18 June by Roger Dicken, the special-effects expert who made the "beastie".
"The alien was a very simple model, although it had to be very lifelike," Mr Dicken said.
"He had a lot of workings inside a very small frame. So if anything had gone wrong we would have been in great trouble ... It is the actual creature which came breathing, pulsating and screaming out of John Hurt's chest."
That special effect was no easy thing to achieve. "I was positioned under the table on which John Hurt appeared to be lying, although in fact his body went through the table to create the effect," Mr Dicken said. "I operated the beast with my right hand, pushing it up through a false chest- piece fitting to John Hurt and filled with animal intestines and blood pipes from an abattoir.
"Simultaneously, I pumped the creature's chest with an air tube in my left hand and various assistants squeezed other air tubes that I'd fitted running through the middle to activate his tiny arms, gills and saliva.
"It was not remotely scary in real life. Although the beastie obviously created a bit of film history, I do feel he was the least artistic of the many things I've created."
Mr Dicken, a veteran of the Dr Who special-effects department, now makes fantasy figures for collectors. "I've got no time for the horror movies of today," he said. "There's far too much gratuitous violence and hype and there's an awful waste of money