Having lived here for 9 years now, we have never had a bat in the house before. This last week we have had one on two separate occaisions, flying in circuits around an upstairs bedroom! The second time one flew past me as I watched TV and went on upstairs! Both looked like pipistrelles. There is a roost next door and I have seen bats enter a hole in our back wall before now. I remembered reading an article in the latest (timely) RWT newsletter on what to do in such an event. I opened the windows as widely as possible (whilst the bat flapped around my head), switched the lights off and closed the door. An hour later it had gone.
I read that young bats are most likely to enter your house between mid July and mid-August as they have just started flying and lack practice! I think the bats had probably entered the house at dawn, and roosted inside during the day – only to become active once we had shut the windows and doors for the evening.