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Look at the leaves, at the base of the plant.
1)if bright shiny green, G. woronowii.
2) if grey-blue and narrow, and pressed together like two hands in prayer, it's G.nivalis. (as you have here)
3) if grey-blue and broad, and:
a) pressed together like hands in prayer but with the leaf edges folded back underneath, it's G. plicatus.
b) or if wrapped around each other, it's G. elwesii.
Obviously there are hundreds (thousands?) of cultivars of snowdrop out there, but unless you are at a Galanthophile convention, you will probably be happy to just get them into one of these four categories.
Oh, and there's an unrelated plant, Spring Snowflake (Leucojum vernum) which is generally bigger and fancier: just google the name and look at pictures of it, you will easily see the difference between it and proper snowdrops.
Hope that helps!
How to take close-ups with cheap phone and hand-lens:
Field Guides for Budding Botanists:
... a lot of the cultivars are hybrids.
(But I've been happy enough to record all the sites I've seen - apart from a couple of woronowii - as nivalis. I hope this year to get them consistently recorded as f. nivalis and f. pleniflora.)
...about the hybridisation, I didn't want to get too confusing about it.
Presumably you mean to separate your G. nivalis and your G. nivalis 'Flore Pleno'?
I can't decide which I prefer - the sheer beauty of the Flore Pleno double frilly flowers, or the classic elegance of the ordinary ones!
Lat/Lng: 54.1483, -4.5245
OS grid ref: SC352754
In a garden near the pavement.