Theres definately no electric windows blanking plate, and the grill for
the
tweeter is part of the enclosure. I can only find one screw, at the bottom
and its not covered as you described. I'll take a photo later to explain
better, but what your describing sounds very different.
There's no tweeter in there at the minute, I intend to fit one.
Thanks for the help anyway, I have a feeling the top part clips in but I
daren't just yank it for fear of breaking it.

Here a link to the photo I took. Hope this helps to explain what I mean.
http://homepage.ntlworld.com/d.mills2/door_handle.jpg

Andy M