Presented here is one of the original Chestbursters made (and manipulated) by Roger Dicken for Ridley Scott’s film.
This prop was co-created by Dicken and Scott during numerous work sessions at Dicken’s house, also known by the crew as the «Witch House». Giger’s only contribution to the design was the add of small limbs on both sides of the creature.
I believe only 3 were made for the film: One very simple version, made of hard material, for the scene where the Chestburster rips through Kane’s chest. A second one, the Hero model, fully articulated and detailed for close-ups (this one was sold in 1996 by Phillips Auctioners). Finally a third one, presented here, very similar to the hero model but not articulated at all. I believe this one was intended as a stand-in for the Hero model, and maybe also for use in the scene where the Chestburster runs away from the shocked crew of the Nostromo.
The previous owner told me that this long-lost ALIEN artifact re-surfaced in the UK at an attic clearance something like a couple of years ago. He found it in a box full of vintage metal Dinky toy cars.
Since the start I’ve been inclined to believe his story because of a few simple facts :

1- That’s also how the original ALIEN clappers were found years ago. Crew members used to take souvenirs home after production wrapped. These kind of (true) stories have been heard many times.

2- The prop is made of polyurethane foam coated with a latex skin. Due to bad conditions of storage the foam as inflated and in the process deformed the shape of the prop, but it’s still recognizable. The overall proportions and, most important, some details are still here despite the years. This prop as nothing to do with any kit or garage kit released by diverse companies through the years. Anyhow all the kits were made of soft vinyl (original kits) or resin (recasts), not polyurethane and latex.

More important, I’ve been able to definitely identify the provenance of that prop thanks to two photos taken during production of the film in 1978 :

Photo 1- The support at the base of the prop can be spotted in a photo of the Chestburster taken on set. It’s a wood support covered with a metallic tube. I believe the Chestburster presented here is the one shown on that production photo. That support was here to allow simple manipulation during the scene where the Chestburster runs on the table : Dicken was holding it from under the table by its support.

Photo 2- Red pigments can still be spotted on the tail of the prop. Now if you look at that photo of Roger Dicken posing with his creations you’ll notice that the tail of the Chestburster (the Hero one) also has red pigments on the same areas of its tail. It’s interesting , and logical when you think about it, to note that the tails of the Chestburster and Facehugger came from the same sculpt.

That’s why I truly think this prop is genuine.
In order to preserve it the best possible way for future generations (the poor thing has suffered enough !), I have asked Tom Spina Designs to provide some restoration work on it. I must say that the result, when you see it in person, is stunning ! Thank you guys !
(The three photos of the prop on white background are courtesy of Tom Spina Designs)