I don't have the label but can describe it as being an inch by half an inch, clear plastic, and with "Marks & Spencer" in their typical font and "St Michael" in their typical italics below that. All print is black. My guess - because of the label being clear plastic, similar to 1980's Wedgwood labels - is that it might be from the mid to late '80's. It also has the general look of a label dating from around that period (I once worked in the labelling industry for just under 10 years).
1990's cannot be ruled out, but the general shape of the vase itself is so similar to some 1980's Wedgwood designs.
One thing for sure is it's definitely not 21st century, as M&S ended "St Michael" in 2000.
Any further help greatly appreciated. I no longer have the vase but am still interested.