[scipio]

Thank you both for your thoughts. While I have tried understand the technique (I have avidly read the books) I have absolutely no practical experience (apart from a couple of bat walks:-Pipistrelle in Ireland and Daubentons in Winchester). That is where the frustration comes in.
This bat ticks some boxes of one variety and some boxes of another. e.g 22Khz and even pulses= Noctule, whereas chip and no chop and flying at lower levels= serotine or leistlers.
It certainly doesn't fly as high as swifts. We are in a wooded area and it flies below the tree tops and often below or at the eaves. If I point the detector out of a bedroom window I swear I can hear its wings flapping (through the headphones) when it gets close. It (if its the same one) seems to appear as early as 19:30.
I guess I must go on more bat walks with the experts