Common shiny woodlouse
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I'm no expert but the shape of the plates at the animal's rear seem to be distinctive of this species
The single woodlouse is definately Oniscus asellus. As Bob says it is the shape of the abdomen (pleon), it is the same width as the thorax (pereion). This gives the general appearance of smoothness to the animal's contour. In the simialr species, Philoscia muscorum (striped woodlouse) the pleon is much narrower breaking up the smooth oval shape. Also, as the name implys a fresh animal has a single stripe down it's back; however this does not always show.
It is hard to say from the photograph but the second animal from the right in your second photo could be P. muscorum. When I blew up the photo in photoshop it appears to have a line down the back and a narrow abdomen.
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Dear Graham, we'll try to get a better pic if we find them again!
Lat/Lng: 53.465066866632, -2.2487149536937
OS grid ref: SJ835965