I was digging the borders in the garden recently, and amidst the stones, weeds and other bugs, I found a millipede, though I couldn't tell you what sort. My brief research suggests there are at least 50 UK species of millipede and they can be quite hard to tell apart. It was about 30mm long I'd say.

The photo above (click for larger version) shows the little legs working away underneath in a wave like motion up the body. Millipedes have two pairs of legs per body section, easily seen here, whereas centipedes only have one pair per section. As always, click for bigger version. That's a gardening book in the background – always a lot to learn!