Clearly a leech, but what species?
Mouths at both ends.
Overall length (dead) 152mm.
Colour, a uniform dark green with occasional small spots a little lighter.
No interactions present.
...medicinal - Hirudo medicinalis - do you know how many eyes it has this also helps ID.
If you move this observation to invertebrates you stand a better chance of getting an identification. You can use the edit tab at the top of the observation.
Lat/Lng: 51.5, -0.126
OS grid ref: TQ301795
Found (dead) in a new hole made builders.