About 3cm long. Moves very fast. Found under stones/logs.
No interactions present.
Many thanks for all the ids. Might be a while before I commit those names to memory, especially the millipede. :)
Maybe I mixed up the size - I'll try and get something in the picture for scale next time, but they do run off very fast.
Lat/Lng: 52.1, -1.6
OS grid ref: SP3350