Mason bees

On the subject of bees.  In late summer we get masses of bees circling around the edges of the veg patch soil, burrowing into single bee sized holes. Going quite deep as the spoil from their burrows is subsoil colour.  They are very busy and benign.  Anyone know what type of bee they are?

I second Bren's guess. They're solitary bees that like to nest in groups - each female digs a vertical burrow with several cells branching off in which they lay their eggs.

Here's a female tawny mining bee (Andrena fulva) that I photographed a couple of years ago:

   

The males are harder to identify as they're a buff colour, similar to several other species.