Orange. Brown stripe along length of back. c20mm. c18 body segments.
No interactions present.
There are around 56 species of millipede in the UK. I've never seen one like this before. I'm not sure which species it is, I tried to key it out from your excellent photo, but failed!
56! No wonder I couldn't find a match. I noticed after posting pic that my beastie seems to have less 'waist' between segments than P complanatus illustrations I've found.
Thanks for that Jon, makes it more exciting.
Lat/Lng: 51.224166, 1.193705
OS grid ref: TR230520