White/Pink form of Greater Knapweed.
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You're right Mushroom Lady. It is Greater Knapweed. Annoyingly my ref book shows Centauria nigra and C.scabiosa on different pages, thus I couldn't compare the two. But I can see now how easily distiguishable they are following your advice. Thank you.
No, Chris was right first time - this is C. nigra var. radiatus - the leaves are clearly entire and not lobed like in scabiosa. Some nigra populations have a lot of this form, others none
Lat/Lng: 51.45093, -3.19346
OS grid ref: ST171731