Despite how it looks, and also how it was flying when I saw it, this is not a bee.
It's a hoverfly, and I was drawn to it by how unusual I thought it looked. I had never seen one before, and I thought it was a bee, but the eyes weren't quite right.
I posted it on a forum and should thank my pals from the JREF forum for helping me to identify it.
It is standing on something I actually see quite a lot - good scottish thistle.