black - many segments -longer than beetle -but not as long as a millipede - wriggled out of sight quickly
No interactions present.
It could be a rove beetle (Staphylinidae). The elytra (wing covers) of many rove beetles cover only some of the segments. 'Quick wriggler' is a good description of how rove beetles move.
Lat/Lng: 50.756, 0.179
OS grid ref: TV537974
on short grass near Beachy Head