Flowers deeper purple than lilac Creeping Thistle nearby.
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Looks a bit too tall to be C.dissectum. Also the clustered flowers atop the stem look more like C.palustre to me. C.dissectum flowers are usually solitary. I think I can see spiny winged projections on the stem too.
Looks like a marsh thistle with those clustered flower-heads. Meadow thistle has solitary flowers with silvery stems. Marsh thistles look untidy, meadow thistles always look strikingly graceful.
Thank you to both of you. It was not marshy so that put me off!
Certificate in Contemporary Science (Open)
Lat/Lng: 51.0884, -0.6977
OS grid ref: SU913329