Bats

There was a bat in our bedroom at 11pm last night - it made me jump, though I've never minded them. I always put the light on as I walk into the room, and the bat was fluttering round and round at about my eye level; I quickly put the light out, closed the door and went down again for assistance. Paul went to put the outside yard lights on and I went back to open the window wide - it was already open about 6". The bat circled again, but as soon as I moved away from the window it flew out. It was big, I wonder what sort it was.
That's the third time in 21 years that we have had a bat indoors. There was one on the hall ceiling once, which went out on its own, and one that was settled on the bathroom washbasin; it looked like a crumpled piece of black velvet. I picked it up in a duster and launched it from the door (because they are supposed not to be able to take off from the ground - I suppose that's why it was stuck, having landed on the basin).