I would agree with Wuff that the Dartington sandblasted mark (shown in Mark Hill's small booklet) does look different to the mark on my glass.

I think the jury is still out.

having just written the above, John has attached something that I was going to attach, for comparison - the backstamp from my vase the other day - which incidentally, Linda Smithson has today confirmed as post FT (some time in the 1990's) - so no FT No. (so Jackie was correct).
I have the drinking glass and the vase in front of me - and there is no doubt that when compared these backstamps are very different in size and outline.
If the vase was produced during the '90's and the cut drinking glass at a similar time, you'd expect the backstamp to look similar. However, I suppose if the pieces were made at different places, then maybe the workers had access to backstamps of differing format/style or whatever.
I don't know when the 'Justine' range of cut wares was produced, or even if this pattern is from that range - it looks similar, but.............