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Found this grass today in local grassland (!) close to bank of watercourse. There is purple at the base but not in clear purple stripes.
Slightly purple at base, not in clear purple/white stripes though so a little hesitant but this may be correct for Winter ID, I'm not very experienced.
I can't help with an id as I'm not very good at grasses yet(!), but I can recommend a good book called 'Grasses, Ferns, Mosses and Lichens' by Roger Phillips - lovely clear photos that may help you id your observation. Good luck!
Lat/Lng: 50.5483, -4.2999
OS grid ref: SX371745