Prototype Light Anti Gas Respirator ?????

[GasMasksUK]

I've had this mask in my collection since summer 2007, it was a bargain at £10.00 and its the only one I've ever seen throughout my few years of collecting. As far I know at the moment its a one of a kind mask because none of the more dedicated collectors with 800 plus masks in their collections have ever seen one of these. It was even almost destroyed by accident, by a postman who thought he would be helpful and put a note through my door and leave in in my bin when I was on holiday

Fortunately a neighbour checked the bin just incase, and it was recovered

So I was wondering if anyone here has came across any more of these in the past or might have information on it. So far I've established that it was made by Seibe Gorman, and its possibly a prototype. Its in its original box, well part of it anyway, sadly the top is missing which probably held the clue to the history of this mask

Thanks

Danny