I have sent two further pics of these little creatures to see if anyone can give me an id. They are about 8mm long. They are using the small holes in the 'bee post' and are sealing the holes. They are in my garden at Five Oak Green, Kent.
Thanks for the confirmation. I also got some shots of them gathering resin from a knot in the gatepost only six inches from their tunnels. I have put the 'bee-posts' in the garage away from rain and snow and will put them out again in spring. I am intrigued as to how the youngsters dig their way out. This has been such a privilege to see these pretty little bees working so hard.