Small holes and mounds in grass.

Can anyone shed some light on what could be making these holes please? There are probably 10 in any one square meter... For scale, these mounds are about the size of a 50p.
Thanks

 

Probably a mining bee.

Some info here.

Mining bees, mason bees, carpenter bees,

 

@Bob Duckodil I they look like the holes of mining bees. They like undisturbed soil. I find them in the onion patch and on the raised Mediterranean bed as well as the grass.
See here for more info Guide to Solitary Bees in Britain | The Wildlife Trusts also Solitary Bees

 

Oh great, thanks for the replies