Found on edge of woodland path in Bryngarw Country Park
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You do not show if the stigma is 4-lobed and the look is of E. obscurum or ciliatum. E. montanum would have more obviously broader leaves.
Unfortunately there were no fully-developed flowers on the plant to photograph or examine, but I will review the photos against the 2 suggestions you have made and make an alternative selection. Thanks again for your feedback on this and other observations - I hope I am learning more each time.
Happy to accept advice that it is more likely to be Obscurum or Ciliatum than Montanum, but not sure it is possible to determine which. Main leaves don't seem to have much of a toothed edge and appear hairless. The stems don't have 4 very obvious raised ridges, as Rose's Key suggests Obscurum should have. Have therefore "plumped" for Ciliatum.
Lat/Lng: 51.5524, -3.5785
OS grid ref: SS906849