Identified today, though actually seen a few weeks back.
On a night ride, lots of screaming noises and rustling from the bank at the side of the track. Shone my lights in and saw a badget humping away - not uncommon. But something with two sharp teeth, flat nose, small eyes and big head started at me for a moment, then bolted.
Couldn't work out what it was - I thought Otter, but here in West Sussex? Nah...
Ferret? Too small. Finally decided it must have been a cat, and a trick of the light.
But just got told on a bike ride that yes, otters have been seen in the area - so seems it really was an otter!