Unknown wasp or bee nest

Unknown wasp or bee nest

Observation - Unknown wasp or bee nest - UK and Ireland. Description: Can anyone help me identify the bees or wasps that are making this nest, please? It is in my garden. They have excavated a sizable cavity in the earth. There are little balls of earth strewn at the entrance, and I can see them carrying them out. There is

Can anyone help me identify the bees or wasps that are making this nest, please? It is in my garden. They have excavated a sizable cavity in the earth. There are little balls of earth strewn at the entrance, and I can see them carrying them out. There is a tremendous amount of activity, they are coming and going every few seconds. They are quite small; much smaller than bumble bees. I assume they are a species of wasp, but I had no idea that wasps excavated cavities in mud.