Hi Any help gratefully received, I found this in my garden in Surrey. Despite many a bug hunt with the grandkids I have not come across one like this before. Sorry I didn't size it but we are trying to instil the idea of look and quick release into the youngsters. It was about twice the size of the more usual ones.
I don't know anything about woodlice species, but it loks as if this one is ready for moulting, with the old exo-skeleton alraedy detaching on the anterior segments but still firmly attached on the posterior ones.
Paul is of course correct - this woodlouse is in the process of molting. Woodlice cleverly molt in two sections, the back half first followed by the front shortly after; this ensures that at least half of their exoskeleton is in tip top condition and hard enough to provide adequate protection.
This one looks to be the Commom Pill Woodlouse, Armadillidium vulgare.