What animal is this?

[Southern-Gal]

Twice now Ive seen what looks like a mink type animal by the road.
It is dark brown all over, bigger than a stoat and bigger than a domestic ferret.
It has a fluffy tail and looked to be all one colour, dark chocolate brown. When it runs it bounds like a ferret.
Ive spoken to someone else who has also seen them but what are they. It was rolling about on the grass verge and did not have a pale underside to its belly.
Had a look at a wildlife book and the nearest I found was a mink but its tail was not in the picture.
Has anyone else seen them and what are they?
Both times I have seen them in the morning, just before 9am.