Oh AC
Sounds like a rat and its the time of year when they are in their nests for the winter period.
I had them years ago under our garage and the tunnels were into our garden another into the greenhouse and two other tunnels into both neighbroughs garden.
Their nest may be in your neighbroughs garden and one of the tunnels is comming up in yours.
Our neighbrough here said rats would tunnel from his neighbroughs garden on the right under his and come out in ours ahhhhh but that was 25 years ago the woman who lived here would put cooked food on to the compost heap.
He put it down to having dogs thats why the rats would not come up in his garden.
Jeyes Fluid or pee down the holes that might make them choose a different place to surface.
I was told that rats have winter and summer houses so they will be moving out when the better weather comes. But will be back next winter? this came from the rat man who I was on first name terms.
Now hasent that cheered you up AC.
