Thank you Sue for unashamedly bumping this thread.
Re the Sharon glasses, as far as I can tell they were originally designed (in 1970) as plain glasses but are shown in a 1986 catalogue in three different cut styles. Mine are plain, yours sound like Sharon Flat Cut (FC), also shown is Sharon Eastern Promise with swirling cuts (EP) and Sharon Regatta with diagonal cuts (REG). All with matching decanters.
The dimensions of the claret glasses and champagne flutes is similar, though the flutes look a little more slender. The wine goblets are bigger again and the sherries smaller.
Information from Dartington Glass, The Art of Frank Thrower, the First Twenty Years (ISBN 978-0-9556095-0-3).
FT115/1 - sherry.
FT115/2 - claret.
FT115/3 - goblet.
FT115/4 - champagne.
So the full nomenclature for your glasses Sue would be FT115/4 FC.