Solitary bee / wasp holes?

Solitary bee / wasp holes?

Observation - Solitary bee / wasp holes?. Description: Found on an ex colliery site. Please can anyone help identify the species or group likely to have made these holes? Hopefully you can see from the photo that the entrance to the holes had been built up with mud and was raised above the ground surface

Found on an ex colliery site. Please can anyone help identify the species or group likely to have made these holes? Hopefully you can see from the photo that the entrance to the holes had been built up with mud and was raised above the ground surface