Lens cap 55mm in diameter.
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Thanks Roger. It really is a pretty and dainty plant. I was very pleased when I found it but hadn't a clue as to it's ID.
My blog: http://wolvobirder.blogspot.com
because there is a lot of size variation; and the number of flowers in the head can vary as well - sometimes there is a full head of bright blue-purple flowers,in other plants - like here - they've mostly fallen off.
Lat/Lng: 52.4985, -2.2411
OS grid ref: SO837889