Question Author
Chuck:- The BT Vision remote is configured to work the tv as well as the bt box, so the volume buttons work the tv volume control.
In the time since I posted this question I've been on the radio and telly forum pages and have found this problem has been around ever since bt vision first came out and there is apparently no pot. in the box to adjust the volume levels and no way for the user to do anything. I suspect that it might be adjusted by the software updates that bt send down the broadband line when they really want to muck everything up.