I feel like I've seen these here before.....any ideas?  

they are van Os chairs so called Swing which you can see they do "swing|" the family van Os had their own factory/shop in culemborg Netherlands there were a lot of shop/facotry's thereThey are attributed to both C.J and also G.J.van os father and son dated 1949
you should chek if tehe back is intact or broken take the 'head' and the 'knee' and press yous arms together if it moves to much ist broken and practicaly worthless
maarten van wesemael

Thank you wesemael! I knew I had seen them before, once you commented I remembered I had seen them in a shop in Amsterdam. I'm going to see them at the weekend if they're still available!