Small spherical grey segmented creature. found within a rotting trunk.
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I always called these pill louse and it is, I imagine, closer to a wood louse than a millepede.
Just found Wikipedia reference which seems to concur with the original posting, ie, that it's a pill millipede rather than a pill louse. See http://en.wikipedia.org/wiki/Glomeris_marginata
Yes, it's a pill millipede. One of the things to look out for is the shape when rolled up - pill woodlice (of which there are several species) are more or less circular when rolled up and viewed from the side, whereas pill millipedes have a flat edge when rolled up and viewed from the side (shown well in the first photo above).
There are three species in the pill millipede family, but Glomeris is the only large one. The other two are tiny and pale in colour, and not often encountered.
Entomologist and biological recorder
Thanks Everyone, I had a feeling that this wasn't a Woodlouse.
Lat/Lng: 52.6, 1.4
OS grid ref: TG3306