Solitary Bee ID help needed

Solitary Bee ID help needed

Observation - Solitary Bee ID help needed - UK and Ireland. Description: Solitary bee nesting in a 8mm hole drilled in a block of gritstone approx 4 foot off the ground. Blocks holes with mud. Much more grey in colour than (probable) red mason bees in the area.

Solitary bee nesting in a 8mm hole drilled in a block of gritstone approx 4 foot off the ground.
Blocks holes with mud.
Much more grey in colour than (probable) red mason bees in the area.