I was out with Dylan round the local lake, Whitlingham Broad, in the dusk tonight and they were fizzing about all over. They seem to fly for fun, though in reality they are on a serious mission echolocating insects. Still, it is joyous in the air. I think they are Daubenton’s Bats, but I’m not certain: they look pretty much like this brilliant photo I found on image search.
Stephen Foster's Blog 
We have lots of different bats around here, they are wonderful creatures. Much misunderstood and well worth learning about!