Thanks for taking a look M.
I had a look through the exhibition photos a while back and wasn't sure my vase was shown. Some of the pieces are hard to compare, if I'm looking at the same vase, I think the brown example you mention has a 3 pronged triangular base, whilst mine is completely flat with the central inverted spike ?
There are a couple of other vases shown which also look similar (with a flat base) however, not sure the spike is the same, also some appear to taper slightly towards the top of the vase, whilst mine is completely cylindrical.
I had a scan through one of the mid 70s catalogues and also couldn't see an exact match. I'll have another look around, fingers crossed.
Many thanks,
Greg