Animal burrow under doorstep

Animal burrow under doorstep

Observation - Animal burrow under doorstep - UK and Ireland. Description: Mice have been living under this doorstep(approx 3 foot x 4 foot) for a while now but we've recently found this hole. It is about 3 in diameter and seems to have been dug from the outside. Also found a similar one going under the shed. Any ideas what it

Mice have been living under this doorstep(approx 3 foot x 4 foot) for a while now but we've recently found this hole. It is about 3" in diameter and seems to have been dug from the outside. Also found a similar one going under the shed.
Any ideas what it might be please?