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Lepidochitona cinerea.Lacks the tufts of bristles of an acanthochitina.The photo's so sharp you can make out the granules on the girdle & the yellow band round it is the 'flat spines' you can almost see.
(& most importantly it wasnt a very low tide, ruling out all the other chitons)
Oh right, I thought the white bits around the edge were the bristles, i just went by the two seashore books i had with me and googled images to compare.
Lat/Lng: 55.6082, -5.1295
OS grid ref: NS029393