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There have certainly been disarticulated woodlice in the immediate vicinity and in the past I have been tempted to pin the blame on Blaniulids (e.g. iSpot Search: Stockway Blaniulid). I have been carrying the impression that plates of disaggregated woodlice always appear white but I’ll try and explore this further.
I checked today and the objects are clearly fragments of what could well be a woodlouse’s outer layer. (I have just read* that this is not made of chitin but is based on calcium carbonate – the basis, I presume, of the cuticle being more permeable to water: * http://www.gardenersworld.com/blogs/wildlife/in-praise-of-woodlice/2663.....)
Another possibility is that these are fragments of a White-lipped Banded Snail (Cepaea hortensis - yellow form) that has been smashed on the stone by a bird)
Lat/Lng: 51.4337, -2.7624
OS grid ref: ST470707