turned over mossy rock in stream - these were under in old moss, with shrimps, been underwater for a good few days, maybe a long time.
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Hi Ken, these look like they could be Cylindroiulus punctatus - (Blunt-tailed Snake Millipede).
Its amazing how long some of these can live like this...heres a pdf of a study of survival under water for various inverts.
Brilliant Christian, thanks very much, that looks right - and for the instructive link, which helps explain why they arent dead!
Lat/Lng: 53.53, -2.05
OS grid ref: SD967037