That's right, it's not a bee. It is a hoverfly but you have to admit it is a very good mimic.
When I looked up its ID, it said that this hoverfly doesn't have a common name so I thought I'd provide a suggestion of Knotter Bee.
Officially, it is Cheilosia illustrata.
How do we know it is not a bee? Look at those HUGE eyes - three times the size of a bee's.
Still not convinced? Check out those antennae (they may be small but it is what it does with them that counts). Bees would have large, thick obvious antennae.