This fourth bee, Andrena cineraria (Ashy Mining Bee), does not strike me as so common here but the reason I am looking is that I do not know for sure. I have found it a few times last week at Pennard, Caswell and last year at Rotherslade.
One thing you might confuse with this is a worn or dark Melecta albifrons (Common Mourning Bee) which is a cleptoparasite of Anthophora bees and lays the egg in their nest whereupon the young hatch and eat all their food. If in doubt, as appearances of bees can vary quite a bit especially when old and worn, look at the wing veins shown in the photo below which can be seen in a good photo from the right angle.
If you are being guided by Steven Falk's excellent new bee book beware that the genera key says the vein indicated by the red line above goes to such and such a position on the second submarginal cell when it should be the third. Not rocket science, easy really!
This book will also help you identify from a good photo a lot of the cleptoparasitic Nomada bees which look like wasps. Here are two flying at the moment:
Nomada fabriciana (Fabricius' Nomad Bee) female, look at the red in the middle of the antennae, parasitises several Andrena but commonly bicolor and flavipes abundant on the coast here:
Nomada goodeniana (Gooden's Nomad Bee) male, again Andrena hosts including thoracica:
Note the shape, colour and position of the yellow spots on the thorax and abdomen. Not all Nomada are this easy though.
A sure sign of strong bee colonies are Bee Flies of the genus Bombylius and this discolor (Spotted Bee Fly) was a long way east, just west of Caswell.
These and other species such as Oil Beetles and Satellite Flies also take advantage of the bee's supplies to rear their own young at the Bee's expense. There is a lot of stealing within the bee/wasp group anyway, they are really interesting to study.
Much more information is available on the BWARS website which also has a link, under resources, to Steven Falk's Flickr pages with a huge mass of pictures and information: