This is Phacelia tanacetifolia, also known as blue tansy. It is a native of the South Western USA but in this country it is mainly grown as a green manure - that is it is dug in to improve soil structure and fertility. It also a wonderful flower for bees.
I have planted a bed of it in my kitchen garden, partly to improve the soil but mainly for the bees. You can see they don't have far to travel.
Phacelia has wonderful navy blue pollen.
Bees value phacelia both for its nectar and its pollen and they behave differently depending on which they are collecting. They seem to do one thing at a time. If they are after pollen they climb through the tall stamens, rubbing themselves against the anthers.
If they are after nectar they are head down in the flowers.
Phacelia attracts other bees including bumblebees and solitary bees such as Hylaeus, the yellow-face bee.
This buff-tailed bumblebee had been collecting pollen elsewhere but couldn't resist the nectar.
The phacelia's flowers are nearly over now so I'll soon be digging it in.